Making serialization functions specific instead of generic and removing helper code.

[xvzcf]

• I've removed the generic serialize and deserialize functions that take in the number of bits to use as a parameter, and replaced them by specific functions that work on 1, 4, 10, and 12 bits only
• This meant the BitVector code was no longer needed, so I've removed that too

[franziskuskiefer]

Thanks!
I left a few comments for some more improvements. If you want to push some of them into followups, just mark them as such.

Please run rustfmt on all the code.

[franziskuskiefer]

Thanks.
I'm approving but please add some comments. When the comments are resolved you can merge it.