Major refactoring.

* Many utility functions moved to tina_util.py.
* Fixed circular import bug.
* A Tinafile is generated between the dry-run and the commit to help
  TINA remember which repos should be tagged, and which pinned.
* A tag type was added to make version bumping and sorting easier.
Merge pull request #5 from RSEmail/cleanup-and-fix

Major refactoring.