Generalize cache -> HDF5 script

Took out hardcoded directory and output file names and turned them
into command line arguments. Also added command line options for enabling
compression via HDF5. An example call:

cache_to_hdf5.py path/to/directory/ output.h5 --complib=zlib --complevel=9
Merge pull request #5 from synthicity/cache-to-hdf5

Generalize cache -> HDF5 script