Afaq Ansari authored Aug 15, 2018 and Katharina Fey committed Aug 15, 2018

* Add enum level to denote different levels of a version value.
Add function to parse input string to enum Level.
Add level parsing test.

* Change the order of assert arms to match tuple value positions.

* Add utility function to bump versions.
Add constants to refer level string values.
Add enum Level.
Add tests for bump_version function.

* Use `match` instead of `if let` for better readability.