replace croaring allocator to RedisModule allocator

[jiangtao244]

Inspired by this.
RoaringBitmap/CRoaring#103 (comment)

[aviggiano]

Hello @jiangtao244 thank you for contributing!
This is a much anticipated wanted feature, so it will be really useful for redis-roaring users (as it helps with #64 and closes #2).

I'll check this out soon, but from what I see it seems correct. The only thing I noticed is that you included roaring.[c,h] on the src files, although it is already part of external deps, so I think they are not necessary. Other than that seems good.

[jiangtao244]

Please review the compile flags and check the benchmarks.

[aviggiano]

@jiangtao244 I have tested this locally and it works fine.
I just added a small change to the PR by removing roaring.h and roaring.c from this repo, since it would be harder to maintain instead of just copying the dependency file from the original repo: https://github.com/jiangtao244/redis-roaring/pull/1

After you accept these changes I will merge this