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/stb.wrap

@@ -0,0 +1,5 @@
+[wrap-git]
+url = https://github.com/nothings/stb.git
+revision = HEAD
+depth = 1
+patch_directory = stb/