Inverse of four_point_transform #273

Would it be possible to add an inverse of four_point_transform? It's an extremely useful function, but a lot of functionality is missing without an inverse.

Give it the image you wish to write to, preferably the same size as the image you got the points from in the first place, give it the transformed (and likely edited image), and then give it the points. Returns the first image with the transformed image untransformed and written to it.