Suggestion for hdf5

[gregoryng]

https://github.com/cgrima/subradar/blob/ff2683639fffa05a541008325b4f3df3e00501da/subradar/simulation/trento.py#L62-L69

        with open h5py.File(filename) as f:
            for key1, item1 in f.items():
                if isinstance(item1, h5py.Group):
                    for dsname, dataset in item1.keys():  # iterate through keys in group, assume it is a Dataset
                        # adding [:] returns a numpy array rather than h5py.Dataset
                        out[key2] = dataset[:]
                        out[dsname] = arr