adding @agmcleod changes + 'screencanvas' extension support
adding @agmcleod changes + 'screencanvas' extension support

@see https://github.com/melonjs/melonJS/pull/190

melonjs/melonJS,TukekeSoft/melonJS,MarkoIvanetic/melonJS,gopalindians/melonJS,srbala/melonJS,Smoss/Enoru-eco,srbala/melonJS,rlugojr/melonJS,srbala/melonJS,TukekeSoft/melonJS,rlugojr/melonJS,melonjs/melonJS,MarkoIvanetic/melonJS,gopalindians/melonJS,rlugojr/melonJS,TukekeSoft/melonJS,gopalindians/melonJS,Smoss/Enoru-eco