Change DisplayObject generateTexture method signature to match Pixijs signature

generateTexture method now matches:
http://www.goodboydigital.com/pixijs/docs/classes/DisplayObject.html#method_generateTexture
Change DisplayObject generateTexture resolution from Int to Float
Overload DisplayObject generateTexture method to avoid having renderer as Dynamic
Made renderer parameter optional for DisplayObject generateTexture method
Merge pull request #8 from aidangrabe/master

Change DisplayObject generateTexture method signature to match Pixijs signature