Add synthetic data to mth5

[kkappler]

There are two synthetic data files in aurora that are used to form mth5 files for aurora's tests. The actual build of the mth5 files does not use any functions from aurora and would be better stored in mth5 (since aurora needs to install mth5).

• [x] add the synthetic ascii files
  • [x] modify setup.py so these files come with pip install
• [x] Consider committing reference MTH5 files
  • [x] Thought about it -- won't do (for now)
• [x] Move tests that build these files to mth5 from aurora
  • [x] The tools to make mth5 from the ascii files can be placed in mth5/data/. This way they are importable to other packages.
  • [x] aurora/tests/synthetic/test_metadata_values_set_correctly.py can be updated to use MTH5 run summary and migrated
    • [x] replace the aurora SyntheticRun class with something that uses mt_metadata.Run
• [X] Migrate the SyntheticPaths class from aurora (to support read only file systems)
• [x] change docstring style to match mth5
• [x] Remove redundant tests from aurora