Add possibility to make intersection of shapes

[ToniaDemchuk]

This library has only simple difference clipping. It would be nice to have other types of clipping (intersect, union).

As I see, you use ClippingLib under the hood and it has support for intersection.

[antonfirsov]

Makes sense, but low priority, moving to Future. Community PR-s are welcome.

[JimBobSquarePants]

On it. See #265