WIP: slowly adding more LMDB API on the C/NIF side
Update to latest async_nif code.
Merge remote-tracking branch 'origin/master' into gsb-finish-lmdb-api

Conflicts:
	c_src/common.h
	c_src/lmdb_nif.c
	c_src/stats.h
	src/lmdb.erl
Update to latest lmdb.c/h from OpenLDAP repo (a05d9910ab2a68806206b00caf71176ada943440 git://git.openldap.org/openldap.git)
Update Erlang glue to latest for async_nif as well.
Update MDB sources from OpenLDAP repo
No further need for khash.h
Update to latest async work.
Minor change.
Integrate current version of async_nif which avoids some enif overhead.
Integrate newest version which avoids the need for a seperate fun.