Move scriptapi to separate folder (by sapier)

On the lua side, notably minetest.env:<function>(<args>) should now
be replaced by minetest.<function>(<args>).
The old way is and will stay supported for a long time.

Also:
Update and clean up lua_api.txt (by celeron55)
Move EnvRef to lua and remove add_rat and add_firefly (by kahrl)
Add separate src/util/CMakeLists.txt, other minor fixes (by kahrl)

src/hud.h

@@ -46,7 +46,7 @@ enum HudElementType {
 };
 
 enum HudElementStat {
-	HUD_STAT_POS,
+	HUD_STAT_POS = 0,
 	HUD_STAT_NAME,
 	HUD_STAT_SCALE,
 	HUD_STAT_TEXT,