Return crate id from match_version

[jyn514]

If I look at where match_version is used, it's always followed by a query on the database fetching the rustdoc_status.
- here we fetch rustdoc_status: https://github.com/rust-lang/docs.rs/blob/master/src/web/releases.rs#L486
- here we fetch rustdoc_status and target_name: https://github.com/rust-lang/docs.rs/blob/master/src/web/rustdoc.rs#L160

Maybe we can change match_version to expose some additional information that makes the next queries easier or, even better, unnecessary?
A simple tweak would be to return the id of the release, making the next query easier.

Originally posted by @koenaad in #565 (comment)

[jyn514]

Mentoring instructions:

• Change the Exact and Semver variants on MatchVersion to have a (String, id) tuple, not just a String.
• Change match_version to query for id as well as version.
• Change the usages of match version (linked above) to use that id instead of crates inner join releases ...

[zeegomo]

Hi, I'd like to work on this if it's still unclaimed!

[jyn514]

@zeegomo go for it! If you have any questions, feel free to reach out here or on Discord. There's also lots of information in the README.