pmemkv 1.2 release

[Szymon Romik]

Hello list,

I’m pleased to announce that pmemkv 1.2 has been released and is available from our GitHub pages.

This release introduces a new experimental engine - csmap (concurrent sorted map, backed by libpmemobj-cpp's concurrent_map).
We have also provided support for custom comparators for sorted engines.

Features:
- csmap engine (concurrent sorted map)
- support for custom comparator for sorted engines

Optimizations:
- vsmap::put() now uses emplace() internally

Other changes:
- test framework refactor (scenario-based tests, extended tests for concurrency and sorting)

Source code and detailed changelogs can be found here:
https://github.com/pmem/pmemkv/releases/tag/1.2 

/Szymon