F2 doc fields

[calbaker]

Added proc macro to create *_doc: Option<String> for most vehicle fields that can be skipped with #[doc_field(skip_doc)] attribute.

TODO:

• make sure *_doc fields are accessible from python
• publish fastim-proc-macros with new version
• fix Cargo.toml path to not be local
• improve documentation in fastsim-proc-macros/lib.rs

[calbaker]

@kylecarow , this isn't ready to merge, but it's a decent idea for you to play with it.

[kylecarow]

After discussion today, it seems we are in agreement that a separate doc struct is the way to go for this