Classifiers are a standard way of specifying a license, and make it easy
for automated tools to properly detect the license of the package.
The "license" field should only be used if the license has no
corresponding Trove classifier.
* Stop using Mr Bump for version handling.
* Only deploy to pypi on tags (not master branch).
* Pick up version number from Travis CI TRAVIS_TAG environment variable.
* Use a better estimation technique to guess text widths.
* Add unittests for validating badge widths for various size badges.
* Add return types to function docstrings.
* Update relevant doctests.
