Add precise frequency mode to BuffrGlitch

[arseniiv]

My implementation of what was proposed in #138.

This is code that wasn’t tested nor built locally so I lay my hopes on CI making sure if it builds at all. Hopefully it should because I didn’t need to use depths of Rust I’m not accustomed with.

Also I tried to write the code according to style I was able to see in this project but if there are parts that should be reformatted, just say so, of course.

Hopefully it does what I intended it to do. And the default behavior should be the old one, the new mode is opt-in.

Also I wasn’t satisfied very much with the mode change applying only on note-on events but that was the easiest way to go without wreaking havoc on the current API, and also it seems pretty reasonable not to mess with a currently played note, and pretty reasonable that the user shouldn’t change the mode back and forth at all.

Well, and also my description in the changelog is probably not very instructive; I’m open for suggestions.

[arseniiv]

@robbert-vdh What can I do for the checks to run? Are they still correctly configured? Didn’t want to bother you before it’ll be clear if this really works but it seems I need to, as some time has already passed with no change. 🙂 And I guess take a look at the code then.