Use JSON-AD parser for deserializing Commits

[joepio]

Currently uses serde, and has nonsensical behavior (only accepts strings, no support for nested resources or arrays).

[joepio]

If I use the JSON-AD parser, I know it will throw because Commits don't have an @id by default. I guess it might be a good idea to give commits identifiers.

I've used the signature of commits + some base URL in identifiers in the past, e.g. https://example.com/commits/YTIfURstCKlYfibyuYUfFyu. If I require this, the one creating the commit needs to know which URL is acceptable - and that means that a client making a change needs to know which route is used for commits. That seems like it could bite me in the future.

I can also just use the signature as the identifier, but that means that they cannot be resolved, because there is no schema. In a way, this is true - a commit doesn't live anywhere yet (until it is validated).

I can also add some conditional to the JSON_AD parser, or create a new function for parsing commits which uses the same logic. That way, Commits still won't have an ID.

I think that feels like the most sensible thing to do. So no new IDs for commits, yet.