The commit fix the issue with concurrent_hash_map_rehash_0_helgrind test

segment_vector: fix typo and doxygen comments

test: fix briefs of concurrent_hash_map test files

Merge back changes from stable 1.7

Fix array_modifiers test

Move containers out from experimental

This fixes warnings generated by doxygen.

and expose range_snapshotting_terator as typdef in containers.

There was an assignment instead of comparison in the test.

Use tx add range flags in vector and string containers

Fix conditional statement for installing segment_vector.hpp

Until now, data in sso was accessed using pmem::obj::array::operator[].
This operator snapshots data which has some performance cost (even
if the data is already snapshotted). This patch change all calls
to pmem::obj::array::operator[] which are alredy preceded by snapshotting
entire sso, by calls to operator[] on direct array of element (_data member).

Rename method to 'add_data_to_tx' and change last parameter meaning.
Now, last parameter is number of elements to snapshot instead of
index of last element.

This test tests that there is no memcheck error during snapshoting
elements (if element have some uninitialized memory).

This flag is needed for objects which are not fully initliazed (for
example pmem::obj::string). Vector always snapshots entires object
and if there are some uninitialized bytes, memcheck will report an
error.