Major refactor to proc macro code

[nicopap]

Hello! Great crate you have here. I'm interested in using it, (actually I'm pushing to use it in bevy, and the community seems very open to it). I discuss why I'd like to use bitbybit in the following PR: bevyengine/bevy#10246

I've a lot of experience writing macros, and I think I can help divide by two the the number of lines of code for the macros. Would you be open to such a contribution?

You can check my coding style in the following files:

• https://github.com/nicopap/cuicui_layout/tree/main/chirp_macros/src

[danlehmann]

Hey, I just merged your patch (f2f986f). Thanks again for your contribution! If you still want to do the refactoring for the main macro that would be fantastic.

Some items to be aware of, in case that changes any decisions on your end:

• I want to some day support non-contiguous ranges (Non-contiguous bit ranges #24)
• For the next major release I am collecting ideas here: Major version bump #51