Add libagg as a subproject

No longer required to be installed, the subproject will be used if not
found.

.gitignore

@@ -1,2 +1,3 @@
 .build*
-
+subprojects/libagg
+sybprojects/lua

lib/font_renderer/meson.build

@@ -1,6 +1,11 @@
-libagg_dep = dependency('libagg')
 freetype_dep = dependency('freetype2')
 
+libagg_dep = dependency('libagg', required: false)
+if not libagg_dep.found()
+  libagg_subproject = subproject('libagg')
+  libagg_dep = libagg_subproject.get_variable('libagg_dep')
+endif
+
 font_renderer_sources = [
     'agg_font_freetype.cpp',
     'font_renderer.cpp',

subprojects/libagg.wrap

@@ -0,0 +1,4 @@
+[wrap-git]
+directory = libagg
+url = https://github.com/franko/agg
+revision = v2.4-lhelper2