Add a way to embed renderer backends code into NazaraRenderer

examples/Std140Debug/xmake.lua

@@ -1,3 +1,8 @@
 target("Std140Debug")
-	add_deps("NazaraOpenGLRenderer")
 	add_files("main.cpp")
+
+	if has_config("embed_rendererbackends") then
+		add_deps("NazaraRenderer")
+	else
+		add_deps("NazaraOpenGLRenderer")
+	end