Merge pull request #565 from bvssvni/master

New internal redesign
Merge pull request #566 from bvssvni/master

Fixed unit tests
Merge pull request #568 from bvssvni/master

Added `PolygonVariant`
Made implementation for `HasSourceRectangle` and `CanSourceRectangle` more generic

Closes https://github.com/PistonDevelopers/rust-graphics/issues/569