Place formal syntax in comments

[vandenoever]

The nom code for parsing would be easier to read if the grammar rules from https://tools.ietf.org/html/rfc3501#section-9 would be placed in comments above each rule.

Here is an example of what that would look like:

https://github.com/vandenoever/rome/blob/master/src/io/turtle/grammar.rs

[djc]

I'm honestly not very motivated to work on this myself. I've tried to keep the parser names themselves close to the formal syntax names, which works well enough for me to keep track of what's going on.

In addition, there's not a one to one mapping between nom parsers and the RFC syntax, because sometimes I felt the implementation would be simpler by refactoring the grammar somewhat.

[vandenoever]

I'm trying to get imap-rust, which uses imap-proto 0.8.1 (nom 3) to work with DavMail and hope to be sending some patches. So far no big ones, but perhaps I'll quote some grammar from the RFC in those patches.

[djc]

Sounds great! I'll review your changes as they come in.