Filled in `convexhull`

[vchuravy]

https://juliaimages.org/latest/api_comparison states that convexhull is the API equivalent to MATLAB's bwconvhull, but it actually returns the outer points of the convexhull and not a "filled in" mask.

Would be great to extend the documentation to actually achieve the same result

[vchuravy]

I have a 3-clause BSD implementation available based on scikit-image. If someone wants to do a clean-room implementation to avoid license confusion. They reference [1] O'Rourke (1998), "Computational Geometry in C",Second Edition, Cambridge Unversity Press, Chapter 7

[ashwanirathee]

I can give it a go since I haven't looked at either of their implementations,though scikit-image implementation shouldn't be a issue as It has been mentioned several time by both tim and johnny,that license contamination issue arises from matlab implementation and scikit's license does create some confusion but isn't a big issue I think

[johnnychen94]

I wasn't aware of this issue before. Given that #24 is also scikit-image based(though it didn't quote the license properly), it should be good to have another one.

[ashwanirathee]

@vchuravy since polygon filling algorithms especially scan-fill which takes verts to fill the image,we just need that here,what do you think? JuliaImages/ImageDraw.jl#53