Add support for 64-bit bitmaps, fix #58

[Ezibenroc]

No description provided.

[Ezibenroc]

Current status:

• All the features implemented in roaring64.h have been implemented in pyroaring.
• Compared to 32 bit version, there misses some minor features (e.g. shift operation), but nothing preventing a release IMO.
• Tests have been implemented, mostly a copy-paste from the 32 bit version, with some minor changes. Note that I did not change yet the range of values covered by the tests, this needs to be done. Tests from the RangeTest are still failing sometimes, due to subtle bugs only appearing with specific values.

[Ezibenroc]

Next steps would be to unify the tests: testing both 32 and 64 bits classes with the same code (with only minor adaptations to handle the specificities of each class). Work in progress.