Split out client code and defs by endpoint type

[David Taylor]

It might be worth splitting up client.rs and defs.rs into sub-paths based on the endpoint type. I think that as the number of supported endpoints grows, keeping all the client code and struct definitions in single large files will start to get in the way: defs.rs is already ~3k lines long.

The best way to do this IMO would be to pull out the client functions and struct defs into sub-paths based on the endpoint type (film, list, etc).