A common complaint about the module API is that modules can't
communicate asynchronously with Emacs.  While it isn't possible to
call arbitrary Emacs functions asynchronously, writing to a pipe
should always be fine and is a pretty low-hanging fruit.

This patch implements a function that adapts an existing pipe
process.  That way, users can use familiar tools like process filters
or 'accept-process-output'.

* src/module-env-28.h: Add 'open_channel' module function.

* src/emacs-module.c (module_open_channel): Provide definition for
'open_channel'.
(initialize_environment): Use it.

* src/process.c (open_channel_for_module): New helper function.
(syms_of_process): Define necessary symbol.

* test/src/emacs-module-tests.el (module/async-pipe): New unit test.

* test/data/emacs-module/mod-test.c (signal_system_error): New helper
function.
(signal_errno): Use it.
(write_to_pipe): New function running in the background.
(Fmod_test_async_pipe): New test module function.
(emacs_module_init): Export it.

* doc/lispref/internals.texi (Module Misc): Document new module
function.

* doc/lispref/processes.texi (Asynchronous Processes): New anchor
for pipe processes.

* etc/NEWS: Document 'open_channel' function.

f3d30b5303 Remove some doc references to old Emacs versions
4217bc229b Fix infloop in shell.el
74b151195d Fix erc-notifications-notify for non-PRIVMSGs, broken in l...
db4436eaf9 Fix the notification action for PRIVMSG in erc-notificatio...
36a4068105 ERC: New maintainer.
2391d3f45d ; spelling fixes
e898442be3 Honor tags-case-fold-search during xref identifer completion

# Conflicts:
#	etc/NEWS

* src/module-env-28.h: Add new module environment functions to
module environment for Emacs 28.

* src/emacs-module.h.in: Document that 'emacs_finalizer' also works
for function finalizers.

* src/emacs-module.c (CHECK_MODULE_FUNCTION): New function.
(struct Lisp_Module_Function): Add finalizer data member.
(module_make_function): Initialize finalizer.
(module_get_function_finalizer)
(module_set_function_finalizer): New module environment functions.
(module_finalize_function): New function.
(initialize_environment): Initialize new environment functions.

* src/alloc.c (cleanup_vector): Call potential module function
finalizer during garbage collection.

* test/data/emacs-module/mod-test.c (signal_error): New helper
function.
(memory_full): Use it.
(finalizer): New example function finalizer.
(Fmod_test_make_function_with_finalizer)
(Fmod_test_function_finalizer_calls): New test module functions.
(emacs_module_init): Define them.

* test/src/emacs-module-tests.el (module/function-finalizer): New unit
test.

* doc/lispref/internals.texi (Module Functions): Document new
functionality.
(Module Misc): Move description of 'emacs_finalizer' type to 'Module
Functions' node, and add a reference to it.

* etc/NEWS: Mention new functionality.

186152ba40 Pacify gcc -Wunused-function on Ubuntu 18.04.3
4cd143aded Fix copyright years by hand
365e01cc9f Update copyright year to 2020
cd2c156163 ; * etc/NEWS: Make the description of XDG fallback more ac...

# Conflicts:
#	etc/NEWS
#	etc/refcards/ru-refcard.tex

Run "TZ=UTC0 admin/update-copyright $(git ls-files)".

59f71d20ea (origin/emacs-27) Fix tar-mode reading the oldgnu Tar format
e3ec84fd7d Ensure mini-window is resized to show active minibuffer co...
450633f85a Fix mini-window resizing under resize-mini-windows = t
219d47893a (emacs-27) Fixes for makeinfo 4.13
4bbfd2b42f ; fix previous NEWS entry
81b697d106 Fix crash under -nw on macOS properly this time
9ce4207969 Revert "Check for GUI frame in ns_color_index_to_rgba"
732dcfc850 Ignore all color fonts when using XFT
aa0c679f48 Avoid unbounded growth of cl-random-state components (bug#...

# Conflicts:
#	etc/NEWS
#	src/nsterm.m

* doc/lispref/customize.texi (Variable Definitions): Fix xref.
* doc/lispref/internals.texi (Writing Emacs Primitives)
(Module Values): Follow xref with comma.

8aad80d661 Fix installer build
47a73e3e14 Update Windows build documentation
cd55984153 Calc: add missing dynamic variable declarations
e8aa6f19e9 * doc/emacs/buffers.texi (Kill Buffer): Improve indexing.
ccd7cd2c51 Speed up dired-do-find-regexp
7edb1f0773 ; Remove outdated declarations
6ab40c1a51 ; Clarify the assumption
be38e39fcc project--find-regexp-in-files: Support remote files
21c3020fce Document some restrictions for module functions.
e1ce9f3423 Don't recommend using 'module-load' for loading modules.
03f962a486 Port x_get_monitor_attributes_fallback to !HAVE_GTK3
0b32f59764 Fix compilation warning in gnus-start.el