Implement support for polygons with holes

[astrofrog]

(like shapely does)

[astrofrog]

@cdeil - I wonder if we could say that PixelPolygonRegion should be a single region and this could be implemented with composite regions?

[cdeil]

@astrofrog - Can we close one of #2 or #3 to focus discussion in one place?

And I don't have an opinion on this question at this point. Just getting any polygons implemented would be fine with me as a first step. Also, looking to ds9 to see what they support / do might be a good idea ... it's seen decades of use and we can just do what they did (if not too hard to implement).

[astrofrog]

I agree on closing one (or both) of them since I think those use cases are covered by compositing.

I'm spending 1 hour now to try and see how hard getting polygon support in is.

[cdeil]

I agree on closing one (or both) of them since I think those use cases are covered by compositing.

I suggest to keep one open. At the very least we need a docs section how to achieve this.

I'm spending 1 hour now to try and see how hard getting polygon support in is.

Thanks! I suggest you start by looking at Ginga (see link in #69). Probably we can just copy over the function there for pixel polygon. (and adapt API / add tests / docs ... it's still a day of work) If you put the code, I might try to find time to add tests / docs later this week.