obj: type safety macros and API changes

- new type safety macros with named unions
- atomic allocation API changes:
-- remove pmemobj_alloc_construct()
-- change return values to int
-- return PMEMoid using reference
-- change PMEMoid atomically using redo log
- add TX_NEW, TX_ZNEW, POBJ_NEW and POBJ_ZNEW macros
- add size parameter to TX_ALLOC, TX_ZALLOC, POBJ_ALLOC and POBJ_ZALLOC
- update manpage