Improvements to HDF5-based data I/O
This PR improves the HDF5-based I/O of Array
types, mainly by moving the worker code into the new data.io
module similar to how these things are done for higher-level types.
The subclass types have been modified to import their HDF5 I/O method from this new location, and DeprecationWarnings have been added to the old Array.to_hdf5
and Array.from_hdf5
methods.
Finally, the HDF5 I/O tests for the TimeSeries
have been moved to the Array
test suite for inheritance by all Array subclasses.