pmemkv 1.3 release

[Szymon Romik]

Hello list,

I’m pleased to announce that pmemkv 1.3 has been released and is available from our GitHub pages.

This release introduces a new experimental engine - radix (single-threaded sorted map, backed by libpmemobj-cpp's radix_tree container).

We have also extended the configuration class API and redesigned the optimized version of stree engine.

Features:
- radix engine (single-threaded sorted map)
- config setters with type safety for common config fields
- stree engine optimization (single-threaded sorted map with custom comparator support)

Major fixes:
- fixed operator== in stree engine
- fixed missing checks in move assignment operators

Other changes:
- operator<< for pmem::kv::status

Known issues:
- vcmap (github issues #623, #798)

Source code and detailed changelogs can be found here:
https://github.com/pmem/pmemkv/releases/tag/1.3

/Szymon