Instead of constantly making these updates, let's just remove the year
since things are stored in git anyways, and this is not an actual modern
legal risk anymore.
This adds the core unification helper functions that do the core work of
solving the invariants. This includes the actual Unify, OccursCheck, and
Extract which is sometimes known as "zonk".
A few other small functions are also included.
Co-authored-by: Samuel Gélineau <gelisam@gmail.com>