DAOS-VOL

Merge pull request #54 in HDF5VOL/daos-vol from ~NFORTNE2/daos-vol:master to master

* commit 'dabeb538e2feacddeed715670bd87af7d860a4fc':
  Update comments.
  Implement H5daos_get_root_open_object_class
  Add functions to enable user selection of DAOS object class for HDF5 objects.  Fix issue with parallel object ID allocation.  Other minor fixes.