fix KeyValueOserving bug. refer to issue 42
PERFORMANCE: made basic rendering up to 40 percent faster by tweaking Apple internal low-performance.
PERFORMANCE: added optional methods to export an SVGKImage directly into NSData or UIImage with support for Apple's internal performance-optimization / accuracy-reduction flags
Added feature for OpenGL integration: you can flip the output images upside-down to undo Apples incompatible y-axis
Now removing KVO on DOMTree.viewport in dealloc. This is added in initWithParsedSVG and never removed, which causes a leak when an SVGKImage is deallocated.