Make datasets recursive as in hdf5

[miladh]

[dragly]

@miladh What needs to be done for this issue to be closed? Do we have a link to HDF5 docs or an example to test?

[miladh]

With h5py you can do this:

f_hdf = h5py.File("test.hdf5")
f_hdf.create_group("/some/long/path")
f_hdf.create_dataset("/some/long/path/dset", data=np.array([1, 2, 3]))

Exdir gives NameError because of filename_validation

[dragly]

Ah, so this is only about resolving the names. Yes, we should handle that better.