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/fishlim/Makefile.am

@@ -1,10 +0,0 @@
-EXTRA_DIST = LICENSE fish.h irc.h keystore.h plugin_hexchat.h dh1080.h
-
-libdir = $(hexchatlibdir)
-
-lib_LTLIBRARIES = fishlim.la
-fishlim_la_SOURCES = fish.c irc.c keystore.c plugin_hexchat.c dh1080.c
-fishlim_la_LDFLAGS = $(PLUGIN_LDFLAGS) -module
-fishlim_la_LIBADD = $(GLIB_LIBS) $(OPENSSL_LIBS)
-fishlim_la_CPPFLAGS = -I$(top_srcdir)/src/common
-fishlim_la_CFLAGS = $(GLIB_CFLAGS) $(OPENSSL_CFLAGS)

plugins/fishlim/meson.build

@@ -0,0 +1,18 @@
+if not libssl_dep.found()
+  error('fish plugin requires openssl')
+endif
+
+fishlim_sources = [
+  'dh1080.c',
+  'fish.c',
+  'irc.c',
+  'keystore.c',
+  'plugin_hexchat.c'
+]
+
+shared_module('fishlim', fishlim_sources,
+  dependencies: [libgio_dep, hexchat_plugin_dep, libssl_dep],
+  install: true,
+  install_dir: plugindir,
+  name_prefix: '',
+)