RFC: Proposal for bit data

Trying to get feedback on bit-data. I realize that it may not be a 1.0 priority, but discussion on this is still helpful.
If the language had support for bitdata signed and unsigned values (like e.g. `u4` and `i12`), I believe it would be possible to support it through procedural macros. Having said that, I'm not an expert on procedural macros, and honestly - if anyone can write it using this feature - I would love to see it.