Reorganized code into a base type to define the public API and subtypes to implement each backing store.
Updated test cases and fixed some scoping issues in the derived classes
Added beginning of hdf5 support.  Makefile now links hdf5 and the
cm1_hdf5 backend is reading metadata.  The test_cm1_hdf5 case is using the hdf backend and full implementation should be done soon.
Updated makefile