pmemkv version 1.3

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

We have also extended configuration class API and redesigned 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)