Adds split functions for sequence types including lists, vectors, seqs and strings

[Izaakwltn]

This adds splitting by single-character delimiters

[stylewarning]

in the future it might be nice for this to work on any sequence type with any Eq element type

[Izaakwltn]

A few updates on the most recent commit:

• Added the splittable class which has a method split [coalton-library/split]
• Added splittable instances for List Vector and Seq containing elements with Eq instances.
• Renamed the existing string:split to string:bisect
• The new string:split calls split:split on a list of chars.

[stylewarning]

I'm not 100% convinced this is a class we should include. My main reason is that it seems a little contrived: we wanted something generic so we forced it to be. I think the true generic aspect of something that splittable isn't that it's splittable, but rather that elements have a natural ordering (i.e., they can be indexed) and each element can be accessed in finite time.

My recommendation for the direction of this PR is to create a function split in each relevant module (no need to give distinguishing names), forgo the type class, and we can ponder in the future some nice classes to capture such sequential properties.

[Izaakwltn]

Now this merely defines a function split for string, seq, list, and vector.

[Izaakwltn]

No urgency, but ready for review whenever the next PR/Issue cleanup happens.

5/10:

• rebased onto main so it's still compatible
• cleaned up formatting