Removes Either dependency.

[ErisianArchitect]

Description

Either tends to make code a little harder to read, and a little harder to write, so I decided it would be a good idea to remove the dependency entirely and instead rely on tailored enums to do the job.

Related Issue

#609

How This Has Been Tested

All tests passed for all supported versions of LLVM on Windows.

Option<Breaking Changes>

Breaking changes for readability.

Checklist

• I have read the Contributing Guide

(I ran cargo clippy this time, hopefully github actions doesn't complain anyway)

[ErisianArchitect]

Oh, shoot, I just realized that I forgot to write documentation for the new enums. Let me do that real quick before merge.

[ErisianArchitect]

Oh, and CallableValue had Either inside it, so I figured it would be a good idea to replace the Either with an enum rather than replacing CallableValue with an enum. If you think it would be better to replace CallableValue itself with an enum, let me know. I figured there was a reason that it hid away the Either before.

[ErisianArchitect]

I should probably mention: This PR conflicts with #607. I didn't realize that until after I made the PR. For some reason I thought that it had already been merged, so I didn't think there would be a conflict.

[ErisianArchitect]

Any update on this? I'd like to start work on the next PR.

[TheDan64]

I won't be able to look at this until the end of the week

[ErisianArchitect]

Alright, I've got a side project I'm working on anyway, so no rush.

[TheDan64]

Thanks!