Merge back changes from Stable 1.6

[igchor]

This change is 

[pmem-bot]

@pbalcer and @wlemkows please review this pull request

[codecov]

Codecov Report

Merging #291 into master will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #291      +/-   ##
==========================================
- Coverage   96.48%   96.45%   -0.04%     
==========================================
  Files          32       32              
  Lines        2991     3246     +255     
==========================================
+ Hits         2886     3131     +245     
- Misses        105      115      +10

Flag	Coverage Δ
#tests_clang_debug_cpp17	96.44% <ø> (-0.05%)	⬇️
#tests_gcc_debug	96.46% <ø> (-0.69%)	⬇️
#tests_gcc_release_cpp17_no_valgrind	95.56% <ø> (+0.47%)	⬆️

Impacted Files	Coverage Δ
.../libpmemobj++/experimental/concurrent_hash_map.hpp	94.36% <0%> (-1.31%)	⬇️
include/libpmemobj++/experimental/basic_string.hpp	100% <0%> (ø)	⬆️
include/libpmemobj++/detail/life.hpp	100% <0%> (ø)	⬆️

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[kkajrewicz]

Reviewed 2 of 2 files at r1, 1 of 1 files at r2, 1 of 1 files at r3.
Reviewable status: complete! all files reviewed, all discussions resolved