- New Vault::App.hid_to_id and Vault::User.hid_to_id convert Heroku
  app and user IDs into core app and user IDs.
- Fix typo in docstring.
Merge pull request #3 from heroku/hid-to-id

New App.hid_to_id and User.hid_to_id methods convert Heroku app and user IDs into core app and user IDs.