manuals: Remove references to libpngpf(3); update links

From libpng-1.5.0 onwards, the private libpng functions are no longer
accessible to the libpng users, and the content of libpngpf(3) is no
longer relevant.

Update links, introducing the new canonical location of the libpng
source repository:
https://github.com/pnggroup/libpng

2 files changed, 18 insertions, 53 deletions

diff --git a/libpng.3 b/libpng.3
index 2ea6af3b4..04ae7db83 100644
--- a/libpng.3
+++ b/libpng.3
@@ -5995,35 +5995,25 @@ letter, until version 1.0.6j; from then on they were given the upcoming
 public release number plus "betaNN" or "rcNN".
 
 .SH "SEE ALSO"
-.IR libpngpf(3) ", " png(5)
-.LP
-.IR libpng :
+.BR "png"(5)
 .IP
-https://libpng.sourceforge.io/ (follow the [DOWNLOAD] link)
-http://www.libpng.org/pub/png
-
+The PNG (Portable Network Graphics) format specification.
 .LP
-.IR zlib :
+.B libpng
 .IP
-(generally) at the same location as
-.I libpng
-or at
+http://www.libpng.org/pub/png/libpng.html (canonical home page)
 .br
-https://zlib.net/
-
+https://github.com/pnggroup/libpng (canonical Git repository)
+.br
+https://libpng.sourceforge.io (downloadable archives)
 .LP
-.IR PNG specification: RFC 2083
+.B zlib
 .IP
-(generally) at the same location as
-.I libpng
-or at
+https://zlib.net (canonical home page)
 .br
-https://www.ietf.org/rfc/rfc2083.txt
+https://github.com/madler/zlib (canonical Git repository)
 .br
-or (as a W3C Recommendation) at
-.br
-https://www.w3.org/TR/REC-png.html
-
+A copy of zlib may also be found at the same location as libpng.
 .LP
 In the case of any inconsistency between the PNG specification
 and this library, the specification takes precedence.
@@ -6043,10 +6033,10 @@ Libpng:
 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
 Maintained by Cosmin Truta.
 
-Supported by the PNG development group
+Supported by the PNG development group.
 .br
-png-mng-implement at lists.sourceforge.net (subscription required; visit
-https://lists.sourceforge.net/lists/listinfo/png-mng-implement
-to subscribe).
+png-mng-implement at lists.sourceforge.net. (Subscription is required;
+visit https://lists.sourceforge.net/lists/listinfo/png-mng-implement
+to subscribe.)
 
 .\" end of man page
diff --git a/png.5 b/png.5
index 20e6aa70a..9b36f0a0b 100644
--- a/png.5
+++ b/png.5
@@ -18,7 +18,7 @@ Also, PNG can store gamma and chromaticity data for improved color
 matching on heterogeneous platforms.
 
 .SH "SEE ALSO"
-.BR "libpng"(3), " libpngpf"(3), " zlib"(3), " deflate"(5), " " and " zlib"(5)
+.BR "libpng"(3), " zlib"(3), " deflate"(5), " " and " zlib"(5)
 .LP
 PNG Specification (Second Edition), November 2003:
 .IP
@@ -51,34 +51,9 @@ Portable Network Graphics (PNG): Functional specification.
 ISO/IEC 15948:2003 (E) (November 10, 2003): David Duce and others.
 .LP
 Portable Network Graphics (PNG) Specification Version 1.2 (July 8, 1999):
-Glenn Randers-Pehrson and others (png-list).
+Glenn Randers-Pehrson and others.
 .LP
 Portable Network Graphics (PNG) Specification Version 1.0 (October 1, 1996):
-Thomas Boutell and others (png-list).
+Thomas Boutell and others.
 
-.SH COPYRIGHT
-.LP
-This man page is
-.br
-Copyright (c) 2018 Cosmin Truta.
-.br
-Copyright (c) 1998-2006 Glenn Randers-Pehrson.
-.br
-See png.h for conditions of use and distribution.
-.LP
-The PNG Specification (Second Edition) is
-.br
-Copyright (c) 2003 W3C. (MIT, ERCIM, Keio), All Rights Reserved.
-.LP
-The PNG-1.2 Specification is
-.br
-Copyright (c) 1999 Glenn Randers-Pehrson.
-.br
-See the specification for conditions of use and distribution.
-.LP
-The PNG-1.0 Specification is
-.br
-Copyright (c) 1996 Massachusetts Institute of Technology.
-.br
-See the specification for conditions of use and distribution.
 .\" end of man page