Math with Semesters
* You can add positive and negative integers to Semesters : `(Semester("P22") + 3).full_name == "Automne 2023"`
* You can substrate positive and negative integers to Semesters (will return corresponding semester), and substrate Semesters (will return positive or negative integer corresponding to number of semesters between those two)
* All comparison operators between semesters work (lt, le, eq, gt, ge)
**Full Changelog**: https://github.com/larueli/pyutttils/compare/v0.0.4...v0.1.0