Parse prerequisites into tokens

[GabrielDTB]

Prerequisites are written by humans (I think?) and so quite a number of them are irregular, making their parsing into tokens that can be manipulated for various purposes quite a challenge. I don't think it's possible to write a set of rules that encapsulates all of the classes' prerequisites perfectly, but I do believe it's possible to correctly parse ~98% of them. The rest can have manual rules added.

This would allow prerequisite trees and simplifying prerequisites into a single, standard, unambiguous format.

[GabrielDTB]

There is previous work done on this up to f791c49, which is the commit before I began refactoring.

[GabrielDTB]

Might be easier to look into gaining access to and using the workday api instead of parsing these from the catalog

[GabrielDTB]

Another angle is to write grammar on a per-department basis, since grammar is pretty consistent within departments and only starts to differ when you cross over.