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/perl/generate_header.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python3
+
+import sys
+from os.path import basename
+
+out_file = sys.argv[1]
+in_files = sys.argv[2:]
+
+
+def escape_perl(file):
+    ret = ''
+    for line in file:
+        # Escape " and \, strip empty space, shove in C strings.
+        ret += '"' + line.strip().replace('\\', '\\\\').replace('"', '\\"') + '\\n"\n'
+    return ret
+
+
+with open(out_file, 'w') as o:
+    o.write('"BEGIN {\\n"\n')
+    for in_file in in_files:
+        o.write("\"$INC{{'{}'}} = 'Compiled into the plugin.';\\n\"\n".format(basename(in_file)))
+    o.write('"}\\n"\n')
+
+    for in_file in in_files:
+        o.write('"{\\n"\n')
+        o.write('"#line 1 \\"{}\\"\\n"\n'.format(basename(in_file)))
+        with open(in_file) as i:
+            o.write(escape_perl(i))
+        o.write('"}\\n"\n')