This library is based on an STM-specialized implementation of a Hash Array
Mapped Trie. It provides efficient implementations of 'Map', 'Set' and other
data structures, which are slightly slower than their counterparts from
"unordered-containers", but scale very well on concurrent access patterns.
For details on performance of the library see
<http://nikita-volkov.github.io/stm-containers/ this blog post>.