* New file - token_file_processing.py
  - Adds functionality to process, generate and validate token files.
  - Token files are used to confirm if new benchmarking runs are
    required to confirm what (if any) Buildstream commits need testing
    given what was previously tested.
  - Token files also allow checks to be made as to whether the currently
    cached data sets are coherent and whether aborted runs have been
    included.