Reorganize and update the README file; add Markdown formatting

1 files changed, 79 insertions, 81 deletions

diff --git a/README b/README
index 0ef765487..0fdc9b784 100644
--- a/README
+++ b/README
@@ -1,110 +1,108 @@
 README for libpng version 1.6.40.git
 ====================================
 
-See the note about version numbers near the top of png.h.
-See INSTALL for instructions on how to install libpng.
-
-Libpng comes in several distribution formats.  Get libpng-*.tar.gz or
-libpng-*.tar.xz if you want UNIX-style line endings in the text files,
-or lpng*.7z or lpng*.zip if you want DOS-style line endings.
-
-Version 0.89 was the first official release of libpng.  Don't let the
-fact that it's the first release fool you.  The libpng library has been
-in extensive use and testing since mid-1995.  By late 1997 it had
-finally gotten to the stage where there hadn't been significant
-changes to the API in some time, and people have a bad feeling about
-libraries with versions < 1.0.  Version 1.0.0 was released in
-March 1998.
-
-****
-Note that some of the changes to the png_info structure render this
-version of the library binary incompatible with libpng-0.89 or
-earlier versions if you are using a shared library.  The type of the
-"filler" parameter for png_set_filler() has changed from png_byte to
-png_uint_32, which will affect shared-library applications that use
-this function.
+See the note about version numbers near the top of `png.h`.
+See `INSTALL` for instructions on how to install libpng.
 
-To avoid problems with changes to the internals of the png info_struct,
-new APIs have been made available in 0.95 to avoid direct application
-access to info_ptr.  These functions are the png_set_<chunk> and
-png_get_<chunk> functions.  These functions should be used when
-accessing/storing the info_struct data, rather than manipulating it
-directly, to avoid such problems in the future.
+Libpng comes in several distribution formats.  Get `libpng-*.tar.gz`
+or `libpng-*.tar.xz` if you want UNIX-style line endings in the text
+files, or `lpng*.7z` or `lpng*.zip` if you want DOS-style line endings.
 
-It is important to note that the APIs did not make current programs
-that access the info struct directly incompatible with the new
-library, through libpng-1.2.x.  In libpng-1.4.x, which was meant to
-be a transitional release, members of the png_struct and the
-info_struct can still be accessed, but the compiler will issue a
-warning about deprecated usage.  Since libpng-1.5.0, direct access
-to these structs is not allowed, and the definitions of the structs
-reside in private pngstruct.h and pnginfo.h header files that are not
-accessible to applications.  It is strongly suggested that new
-programs use the new APIs (as shown in example.c and pngtest.c), and
-older programs be converted to the new format, to facilitate upgrades
-in the future.
-****
-
-Additions since 0.90 include the ability to compile libpng as a
-Windows DLL, and new APIs for accessing data in the info struct.
-Experimental functions include the ability to set weighting and cost
-factors for row filter selection, direct reads of integers from buffers
-on big-endian processors that support misaligned data access, faster
-methods of doing alpha composition, and more accurate 16->8 bit color
-conversion.
+For a detailed description on using libpng, read `libpng-manual.txt`.
+For examples of libpng in a program, see `example.c` and `pngtest.c`.
+For usage information and restrictions (what little they are) on libpng,
+see `png.h`.  For a description on using zlib (the compression library
+used by libpng) and zlib's restrictions, see `zlib.h`.
 
-The additions since 0.89 include the ability to read from a PNG stream
-which has had some (or all) of the signature bytes read by the calling
-application.  This also allows the reading of embedded PNG streams that
-do not have the PNG file signature.  As well, it is now possible to set
-the library action on the detection of chunk CRC errors.  It is possible
-to set different actions based on whether the CRC error occurred in a
-critical or an ancillary chunk.
-
-For a detailed description on using libpng, read libpng-manual.txt.
-For examples of libpng in a program, see example.c and pngtest.c.  For
-usage information and restrictions (what little they are) on libpng,
-see png.h.  For a description on using zlib (the compression library
-used by libpng) and zlib's restrictions, see zlib.h
-
-I have included a general makefile, as well as several machine and
-compiler specific ones, but you may have to modify one for your own
-needs.
-
-You should use zlib 1.0.4 or later to run this, but it MAY work with
+You should use zlib 1.0.4 or later to run this, but it _may_ work with
 versions as old as zlib 0.95.  Even so, there are bugs in older zlib
 versions which can cause the output of invalid compression streams for
 some images.
 
 You should also note that zlib is a compression library that is useful
 for more things than just PNG files.  You can use zlib as a drop-in
-replacement for fread() and fwrite(), if you are so inclined.
+replacement for `fread()` and `fwrite()`, if you are so inclined.
 
 zlib should be available at the same place that libpng is, or at
-https://zlib.net.
+https://zlib.net .
 
 You may also want a copy of the PNG specification.  It is available
 as an RFC, a W3C Recommendation, and an ISO/IEC Standard.  You can find
 these at http://www.libpng.org/pub/png/pngdocs.html .
 
-This code is currently being archived at libpng.sourceforge.io in the
-[DOWNLOAD] area, and at http://libpng.download/src .
+This code is currently being archived at https://libpng.sourceforge.io
+in the download area, and at http://libpng.download/src .
 
 This release, based in a large way on Glenn's, Guy's and Andreas'
 earlier work, was created and will be supported by myself and the PNG
 development group.
 
-Send comments/corrections/commendations to png-mng-implement at
-lists.sourceforge.net (subscription required; visit
+Send comments, corrections and commendations to `png-mng-implement`
+at `lists.sourceforge.net`.  (Subscription is required; visit
 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
-to subscribe).
+to subscribe.)
+
+Send general questions about the PNG specification to `png-mng-misc`
+at `lists.sourceforge.net`.  (Subscription is required; visit
+https://lists.sourceforge.net/lists/listinfo/png-mng-misc
+to subscribe.)
+
+Historical notes
+----------------
 
-Send general questions about the PNG specification to png-mng-misc
-at lists.sourceforge.net (subscription required; visit
-https://lists.sourceforge.net/lists/listinfo/png-mng-misc to
-subscribe).
+The libpng library has been in extensive use and testing since mid-1995.
+Version 0.89, published a year later, was the first official release.
+By late 1997, it had finally gotten to the stage where there hadn't
+been significant changes to the API in some time, and people have a bad
+feeling about libraries with versions below 1.0.  Version 1.0.0 was
+released in March 1998.
+
+Note that some of the changes to the `png_info` structure render this
+version of the library binary incompatible with libpng-0.89 or
+earlier versions if you are using a shared library.  The type of the
+`filler` parameter for `png_set_filler()` has changed from `png_byte`
+to `png_uint_32`, which will affect shared-library applications that
+use this function.
+
+To avoid problems with changes to the internals of the `info_struct`,
+new APIs have been made available in 0.95 to avoid direct application
+access to `info_ptr`.  These functions are the `png_set_<chunk>` and
+`png_get_<chunk>` functions.  These functions should be used when
+accessing/storing the `info_struct` data, rather than manipulating it
+directly, to avoid such problems in the future.
+
+It is important to note that the APIs did not make current programs
+that access the info struct directly incompatible with the new
+library, through libpng-1.2.x.  In libpng-1.4.x, which was meant to
+be a transitional release, members of the `png_struct` and the
+`info_struct` can still be accessed, but the compiler will issue a
+warning about deprecated usage.  Since libpng-1.5.0, direct access
+to these structs is not allowed, and the definitions of the structs
+reside in private `pngstruct.h` and `pnginfo.h` header files that are
+not accessible to applications.  It is strongly suggested that new
+programs use the new APIs (as shown in `example.c` and `pngtest.c`),
+and older programs be converted to the new format, to facilitate
+upgrades in the future.
+
+The additions since 0.89 include the ability to read from a PNG stream
+which has had some (or all) of the signature bytes read by the calling
+application.  This also allows the reading of embedded PNG streams that
+do not have the PNG file signature.  As well, it is now possible to set
+the library action on the detection of chunk CRC errors.  It is possible
+to set different actions based on whether the CRC error occurred in a
+critical or an ancillary chunk.
+
+The additions since 0.90 include the ability to compile libpng as a
+Windows DLL, and new APIs for accessing data in the `info_struct`.
+Experimental functions included the ability to set weighting and cost
+factors for row filter selection, direct reads of integers from buffers
+on big-endian processors that support misaligned data access, faster
+methods of doing alpha composition, and more accurate 16-to-8 bit color
+conversion.  Some of these experimental functions, such as the weighted
+filter heuristics, have since been removed.
 
-Files in this distribution:
+Files included in this distribution
+-----------------------------------
 
     ANNOUNCE      =>  Announcement of this version, with recent changes
     AUTHORS       =>  List of contributing authors
@@ -153,7 +151,7 @@ Files in this distribution:
         arm-neon/     =>  Optimized code for the ARM-NEON platform
         mips-msa/     =>  Optimized code for the MIPS-MSA platform
         powerpc-vsx/  =>  Optimized code for the POWERPC-VSX platform
-        examples/     =>  Example programs
+        examples/     =>  Examples of libpng usage
         gregbook/     =>  Source code for PNG reading and writing, from
                           "PNG: The Definitive Guide" by Greg Roelofs,
                           O'Reilly, 1999