Piprot

- Merged 51 to avoid a KeyError when stable_version is unavailable (thanks federicobond)

- Fixed 48 where pytz would break everything

- Brings back proper support for versions with different lengths

- Fixed 42 which affected version numbers with more than three groups

Fixed

- vendored the version checking code to fix issue with pkg_resources not being
available

Added

- support for looking up requirements from Github
- support for looking up requirements from a given URL
- Exit status is set to `1` if requirements are out of data (thanks skoczen!)


Fixed

- previously if two releases were released on the same day this wasn't
reported as being out of date.

- updated version checking to ensure that prerelease versions are not included