added buggy cubic bezier rasterizer
fixed bug: wrong iterator for polybez
multi-section clipping of Bezier curve
fixed bug: duplicate intersections

Closes #3
fixed bug: illegal section from bezier clipping

solution: check mid-point of the section
( mid-point can never be outside when the section is inside )
Close #4
fixed bug: duplicate contributions on pixel edge
random test
refactor
implemented line-based contour (i.e. polygon)
implemented quadratic bezier contour
clean-ups
organize modules
added test