Enable mask, shadow and filters on Stage
Merge pull request #91 from xavierhainaux/patch-4

Enable mask, shadow and filters on Stage
Added sourceWidth/sourceHeight setters
Fixed analyzer warning
Use  triple-slash comments
Minor style guide fixes
Removed occasionally defined error codes.

Since we don't have error codes for all possible errors, we shouldn't
use error codes for those few cases where we have defined them.
Added Scale9Bitmap class
Optimized Scale9Bitmap render method
Avoid matrix allocation in Scale9Bitmap render