Allow use of other root group name in h5md_create_obs
Adapt for the change of kind of H5S_UNLIMITED_F between HDF5 1.8.8 and 1.8.11 for Fortran.

Patch proposed by Peter Colberg and revised (addition of parameter H5S_UNLIMITED_KIND) by Pierre de Buyl.
Merge branch 'v1.0_override_obs'
Explicit public declaration.