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

Merge back changes from stable 1.6

docker: bump OS' versions

Heterogeneous lookup in concurrent_hash_map

include make_persistent_array.hpp

tests: fix build

fix missing include header file

docker: bump valgrind version

Extended concurrent_hash_map to support heterogeneous find/count/erase
operations. Our implementation is based on the idea described in ISO C++
paper P0919R3 for std::unordered_map
(http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0919r3.html).

[ 76%] Building CXX object tests/external/CMakeFiles/string_libcxx_modifiers_append_iterator.dir/libcxx/basic_string/string.modifiers/string_append/iterator.pass.cpp.o
In file included from /home/mslusarz/pmem/libpmemobj-cpp/tests/external/libcxx/basic_string/string.modifiers/string_append/iterator.pass.cpp:15:0:
/home/mslusarz/pmem/libpmemobj-cpp/tests/external/libcxx/basic_string/string.modifiers/string_append/../throwing_iterator.hpp:22:11: error: ‘ptrdiff_t’ does not name a type
   typedef ptrdiff_t difference_type;
           ^~~~~~~~~
In file included from /home/mslusarz/pmem/libpmemobj-cpp/tests/common/unittest.hpp:38:0,
                 from /home/mslusarz/pmem/libpmemobj-cpp/tests/external/libcxx/basic_string/string.modifiers/string_append/iterator.pass.cpp:16:
/home/mslusarz/pmem/libpmemobj-cpp/tests/common/iterators_support.hpp: In instantiation of ‘class test_support::forward_it<throwing_it<char> >’:
/home/mslusarz/pmem/libpmemobj-cpp/tests/external/libcxx/basic_string/string.modifiers/string_append/iterator.pass.cpp:196:50:   required from here
/home/mslusarz/pmem/libpmemobj-cpp/tests/common/iterators_support.hpp:184:66: error: no type named ‘value_type’ in ‘struct std::iterator_traits<throwing_it<char> >’
  using value_type = typename std::iterator_traits<It>::value_type;
                                                                  ^
/home/mslusarz/pmem/libpmemobj-cpp/tests/common/iterators_support.hpp:186:53: error: no type named ‘difference_type’ in ‘struct std::iterator_traits<throwing_it<char> >’
   typename std::iterator_traits<It>::difference_type;
                                                     ^
/home/mslusarz/pmem/libpmemobj-cpp/tests/common/iterators_support.hpp:187:60: error: no type named ‘pointer’ in ‘struct std::iterator_traits<throwing_it<char> >’
  using pointer = typename std::iterator_traits<It>::pointer;
                                                            ^
/home/mslusarz/pmem/libpmemobj-cpp/tests/common/iterators_support.hpp:188:64: error: no type named ‘reference’ in ‘struct std::iterator_traits<throwing_it<char> >’
  using reference = typename std::iterator_traits<It>::reference;
                                                                ^

bump clang version required for style check

stdexcept is needed in slice.hpp for std::out_of_range support

Merge back changes from stable 1.6

Style check was conducted even if wrong clang-format version
was detected because var was not removed from the cmake cache

string: append, capacity, erase methods

[1.6] Mark allocation_flag constructor as explicit.

include make_persistent_array(_atomic).hpp in
make_persistent(_atomic).hpp file

Reason: it tests feature introduced with c++20

Call to erase(0) is ambiguous because literal 0 can be treated as integer or null-pointer constant.
Hence equally good candidates in overload resultion are:
- basic_string &erase(size_type index = 0, size_type count = npos)
- iterator erase(const_iterator pos)
We add helper functions to resolve the ambiguity

string: fix size of space needed for null terminator

Fix issue #322