`boost::hash_is_avalanching` in `<boost/container_hash/hash_is_avalanching.hpp>`. Use that header directly instead. `<boost/unordered/hash_traits.hpp>` will be removed in the future.

Added container `pmr` aliases when header `<memory_resource>` is available. The alias `boost::unordered::pmr::[container]` refers to `boost::unordered::[container]` with a `std::pmr::polymorphic_allocator` allocator type.

`boost::concurrent_flat_(map|set)` and vice versa.

Added fast containers `boost::unordered_flat_map` and `boost::unordered_flat_set`

based on open addressing.

The behaviour of swap is different when the two containers to be

Fix a bug when inserting into an `unordered_map` or `unordered_set` using

iterators which returns `value_type` by copy.

Some other minor internal changes to the implementation, tests and

documentation.

Rename overload of `emplace` with hint, to `emplace_hint` as specified in

http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2008/n2691.pdf[n2691^].

`<boost/unordered/unordered_set_fwd.hpp>`.