Implement bitmap-roaring

[fsaintjacques]

See https://github.com/lemire/RoaringBitmap

[pombredanne]

👍 Especially since that could also be the base for a RR Python binding ;)

[fsaintjacques]

I'm actively working on the C implementation. Once it is complete, I'll port it here.

[pombredanne]

@fsaintjacques Thanks! I saw you were in the commit logs, actually I found this project from browsing the CRoaring logs.... I thought I would chime in to inquire. I am happy I did.