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.

concurrent_hash_map: remove dependency from v<>

Remove internal aliases from concurrent hash map interface

Add new data structure: segment_table

Add concurrent_hash_map usage example for doxygen

for consistency with other types.

Refactoring tests to share vector tests between vector and segment_table

Increase timeout for valgrind tests on travis

test_package and test_findLIBPMEMOBJ_cmake runs use libpmemobj 1.4

So that concurrent_hash_map_drd tests will not fail.

Remove unnecessary #include <libpmemobj.h>

Node std layout

remove TTB info from README

Update appveyor to use PMDK v1.7

concurrent_hash_map: introduce internal scoped_lock_traits

it is outdated and redundant

To achieve that classes node and hash_map_node_base was merged into one
class hash_map_node.

to generically implement upgrade/downgrade operations. If scoped_lock_type
implements upgrade_to_writer and downgrade_to_reader then traits class
will just call those methods, otherwise it will provide default implementation.

Fix persistent_pool_ptr swap() method signature

Do not allow concurrent_hash_map concurrent methods in a transaction

to make sure it is consistent in singlethreaded methods like clear()
and assignment operators in case of transaction abort.

All methods that take locks on bucket/elements MUST NOT be called in
a transaction. If this was allowed, transaction could abort after releasing
locks and values would be modified without holding a lock.

Hashmap code cleanup