DAOS-VOL

Merge pull request #157 in HDF5VOL/daos-vol from ~JHENDERSON/daos-vol:master to master

* commit '7479db97bb0496185870a127da5b9e7cd19cd3ad':
  Reset chunk dataspaces after closing them following dataset I/O setup
  Optimize chunk memory dataspace creation for H5S_ALL file dataspace case
  Check for equal chunk dataspaces when calculating recxs and sg_iovs
  Store memory dataspace dimensions for creating chunk memory dataspaces
  Change chunk I/O function to accept a "selected chunk info" structure
  Optimize unnecessary memory allocation in chunk I/O udata structure
  Add I/O cache to datasets