Add subprojects

Instead of relying on host system, some dependencies had been added using meson wrap DB and custom meson wrappers.

Signed-off-by: Piotr Krygier <piotrkrygier@everyonecancode@xyz>

subprojects/packagefiles/stb/meson.build

@@ -0,0 +1,7 @@
+project('stb', 'c')
+
+stb_inc = include_directories('.')
+
+stb_dep = declare_dependency(
+    include_directories: stb_inc,
+)