build: Replace Autotools with Meson

Quick rundown of benefits:

- Much faster:
  - Autotools (with autogen): 22 seconds
  - Meson: 7 seconds
  - Meson (with ccache): 2 seconds

- Simpler:
  - ~1000 lines smaller
  - Single simple language

- Potentially better Windows (Visual Studio) support

What is not done:

- Complete Windows support
- OSX support (easy)

Closes #2013
Closes #1937
Closes #1803

.gitignore

@@ -1,68 +1,8 @@
-# git ignore file
-# Unix generated files
-.deps/
-.libs/
-.dirstamp
-Makefile
-Makefile.in
-aclocal.m4
-autom4te.cache/
-/build-aux/
-confdefs.h
-conftest
-conftest.c
-conftest.err
-config.*
-config-win32.h
-configure
-configure.tmp
+/build
 doxygen*.tmp
 html/
-libtool
-m4/
-plugins/perl/irc.pm.h
-plugins/perl/xchat.pm.h
-plugins/perl/hexchat.pm.h
-po/Makefile.in.in
-po/POTFILES
-po/remove-potcdate.sed
-po/stamp-*
-osx/Info.plist
-data/man/hexchat.1
-data/pkgconfig/hexchat-plugin.pc
-data/misc/hexchat.appdata.xml
-data/misc/hexchat.desktop
-data/misc/hexchat.desktop.in
-data/misc/htm.desktop
-src/common/dbus/example
-src/common/dbus/org.hexchat.service.service
-src/common/dbus/remote-object-glue.h
-src/common/make-te
-src/common/marshal.*
-src/common/textenums.h
-src/common/textevents.h
-src/fe-gtk/hexchat
-src/fe-gtk/hexchat.rc
-src/fe-gtk/resources.c
-src/fe-gtk/resources.h
-src/fe-text/hexchat-text
-src/htm/Main.resources
-src/htm/thememan.exe
-src/htm/thememan.exe.config
-src/htm/thememan.exe.mdb
-src/htm/thememan
-stamp-h1
-*.a
-*.o
-*.la
-*.lo
-*.gmo
-*.mo
-*.po~
-*.pot
 *.patch
 tags
-src/**/*.plist
 # Win32 generated files
 plugins/wmpa/wmpa_h.h
 plugins/wmpa/wmpa_i.c
@@ -79,10 +19,9 @@ resource.h
 *.suo
 *.user
 *.exe
-#OSX
+# OSX
 osx/HexChat.app
 osx/.HexChat.app
-po/.intltool-merge-cache
 *.zip
 *.dmg
 *.VC.db