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

plugins/python/Makefile.am

@@ -1,9 +0,0 @@
-libdir = $(hexchatlibdir)
-
-lib_LTLIBRARIES = python.la
-python_la_SOURCES = python.c
-python_la_LDFLAGS = $(PLUGIN_LDFLAGS) -module
-python_la_LIBADD = $(PYTHON_LIBS) $(GLIB_LIBS)
-python_la_CPPFLAGS = -I$(top_srcdir)/src/common $(PYTHON_CPPFLAGS)
-python_la_CFLAGS = $(GLIB_CFLAGS)
-

plugins/python/meson.build

@@ -0,0 +1,13 @@
+python_opt = get_option('with-python')
+if python_opt.startswith('python3')
+  python_dep = dependency(python_opt, version: '>= 3.3')
+else
+  python_dep = dependency(python_opt, version: '>= 2.7')
+endif
+
+shared_module('python', 'python.c',
+  dependencies: [libgio_dep, hexchat_plugin_dep, python_dep],
+  install: true,
+  install_dir: plugindir,
+  name_prefix: '',
+)

plugins/python/python.c

@@ -69,6 +69,8 @@
 #include "hexchat-plugin.h"
 #undef _POSIX_C_SOURCE	/* Avoid warnings from /usr/include/features.h */
 #undef _XOPEN_SOURCE
+#undef HAVE_MEMRCHR /* Avoid redefinition in Python.h */
+#undef HAVE_STRINGS_H
 #include <Python.h>
 #include <structmember.h>
 #include <pythread.h>