Ref: https://github.com/pmem/libpmemobj-cpp/issues/356

Atomic allocator has limited use case since pmemobj does not allow
for nesting make_persistent_atomic calls.

To make it obvious what is the layout of the structure.

Fix concurrent_hash_map_pmreorder_multiple_buckets test

The check_consistency() function verifies if the hash map contains
elements (0, 0), (1, 1), (2, 2)... starting from (0, 0),
so the first inserted element should be (0, 0), not (1, 1).

Add transaction_out_of_memory exception

Update readme

Use COW support from pmdk-1.6

and catch it whenever obj return error and set errno to ENOMEM.

Merge back changes from stable-1.7

Throw transaction_scope_error in case vector/string ctor was called o…

[1.7] Fix compilation of concurrent hash map test

[1.7] Fix void_t declaration.

Fixes: https://github.com/pmem/libpmemobj-cpp/issues/366

Update test to new hashmap API introduced in: c67264ae

Drop libdir from pkgconfig.

Extend messages in exceptions

Until CWG 1558 (a C++14 defect), unused parameters in alias templates were
not guaranteed to ensure SFINAE and could be ignored, this implementation
of void_t solves this issue. See: https://en.cppreference.com/w/cpp/types/void_t

to message argument. Use those exception in every place where pmemobj error
is handled.

Speed up some DEVELOPER_MODE checks.

cmake: fix tbb detection for distros without tbb cmake integration

There's no binary library to link against.

string: fix memcheck error of uninitialized size field

Merge back changes from stable 1.6