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.

test/GwenOpenGLTest/OpenGLSample.cpp

@@ -356,7 +356,7 @@ int main()
 #ifndef _WIN32
     //we need glewExperimental on Linux
 #endif // _WIN32
-	gladLoadGLInternalLoader();
+		gladLoaderLoadGL();
 #endif
 #endif //B3_USE_GLFW
     //we ned to call glGetError twice, because of some Ubuntu/Intel/OpenGL issue