Handling EIGER h5 files

For the basics please see https://github.com/keitaroyam/yamtbx/blob/master/doc/eiger-en.md.

It is convenient to have DIALS or PHENIX environment, which provides h5py module and bslz4 plugin. To handle bslz4 compression, you first need

import dxtbx.format

which sets HDF5_PLUGIN_PATH.