common: NVML renaming and library splitting

Rename functions in library and split libpmem.
-Rename typdefs: PMEMblkpool, PMEMlogpool, PMEMobjpool
-Split libpmem into libpmem, libpmemblk, libpmemlog, libpmemobj
-Rename trn => obj and add pmemobj fake implementation
-Add benchmark building to make check target
-Change functions _map() to _pool_open()
-Update scope tests
Please, add the comment explaining why we need this custom implementation of `pread()`.