Fixes #230 by adding f/F/t/T

[Kyllingene]

While f was already implemented, this PR implements the rest of them.

Rather than adding Motion::FindBack, FindTo, and FindToBack, I modified Motion::Find to be Find { ch: char, back: bool, to: bool }, and updated the appropriate logic.

[Kyllingene]

Seems like the f keybinding was broken to begin with, and thus so are the rest. I'll do some debugging to see what's wrong

[Kyllingene]

So it seems like, for some reason, the f keybinding and siblings aren't getting parsed properly. I checked the grammar, and the only valid search characters are alphabetical, which is clearly incorrect. Fixing the issue gives me a confusing LALRPOP error that doesn't make sense to me. I'm just going to say for now that this probably does what's intended, but a new issue should be made regarding f that blocks this.

[MrPicklePinosaur]

most likely has to do with conflicts with the grammar, keeping it alphanumerical is probably ok for now

[Kyllingene]

That doesn't fix the issue that it doesn't seem to be parsing correctly anyways, regardless of what character you search for. When you press f, it eats all inputs without doing anything, until you hit escape.