Added GpuCanvas hiearchy
Added == null to check for null pointer
Fixed illegal member access from static function
Changed null pointer check to == null
Moved default use function into base class
Simplified constructor
Added TextureType to OpenGL format helper function
Fixed pixel read function to work with all pixel formats
Added unbind function to unbind FBO texture
Added draw function to draw Canvas in window
Merge branch 'master' of https://github.com/EmilWestergren/ooc-draw-gpu