Generate full crate

[killercup]

My main way of using this would be to run dbc-codegen some.dbc crates/can-messages. The target would probably always be a crate just for the CAN de/encode part, and I'd check that code into the repo.

For that it'd be neat to:

• have the CLI generate the full crate
  • with all deps
  • with a nice readme even
  • maybe even an example file just for fun
• put the "static" content (error types, helper functions) into their own files so they don't change when updating the DBC

As I'm not currently using this however, it is not a prio just yet.

[kilpkonn]

FYI I have some experimentations for something like this here: https://github.com/kilpkonn/dbc-codegen
It is obviously kind of hacky, but likely useful to take as a inspiration/baseline.