move stb_image/stb_image_write.cpp into a cpp file instead of random files with the magic 'STB_IMAGE_WRITE_IMPLEMENTATION' define

move setup.py back to eglRenderer extension, use pkgutil.get_loader('eglRenderer').get_filename()
disable dlmopen by default, unless B3_USE_DLMOPEN is defined.

examples/ThirdPartyLibs/stb_image/stb_image_write.cpp

@@ -0,0 +1,2 @@
+#define STB_IMAGE_WRITE_IMPLEMENTATION
+#include "stb_image_write.h"