test_additional_io: Created a test for the additional_io module. Just tests the function expand_pathname_list. This closes #69.
test_HDF5_searchers: Added a test for HDF5_searchers.get_matching_paths. This fixes #76.
test_HDF5_searchers: Added a test for HDF5_searchers.get_matching_paths_groups. This fixes #77.
test_HDF5_searchers: Added test for HDF5_searchers.get_matching_grouped_paths. This fixes #78.
test_HDF5_searchers: WIP. Added test for HDF5_searchers.get_matching_grouped_paths_found. This is related to #79.