- Fix breaking test.
- Initial work on refactoring logging logic.
- Add tests for Vault::Log module.
- Update logging functionality to be compatible with L2met.
- Add missing docstring.
Merge pull request #6 from heroku/l2met-compatible-logging

l2met-compatible-logging

- `Vault::Log` methods emit L2met-compatible output.  When an
  `APP_NAME` environment variable is present it will be prepended to
  measurement names.

- Tests for the `Vault::Log` module are now in place.

- Docstrings use YARD syntax now.