Support nested structs #18
Description
When the schema of JSON is known, it's likely more efficient to store it as a Rust struct instead. For that to work, we would both need to support single structs as a field, and a vec of structs as field.
Encoding data like that is going to require thoughtful design because we'll effectively be making our own encoding format, as opposed to the work done so far which has relied on Postgres to keep each field separate. It's worth considering if we should use an off the shelf encoding crate.
The format needs to handle field removals and additions, and ideally would also handle field renames.