* No more genericness, only the 32 bit implementation really makes sense.
* Standard serialization and deserialization support as specified in
https://github.com/RoaringBitmap/RoaringFormatSpec
* Massive internal reorganisation, including some visible improvements to the
docs.
* Explicit minimal compatible version of Rust 1.11.0.
* New 64 bit RoaringTreemap added, wraps 32 bit RoaringBitmaps into a
BTreeMap. See http://r-libre.teluq.ca/930/1/Roaring64bits.pdf for a
description (in French) of the likely performance tradeoffs. Contributed by
@bvinc.
