Refactor web::latest_version, move logic into CrateDetails

[yvrhdn]

I noticed web/mod.rs contained a really complicated latest_version function: https://github.com/rust-lang/docs.rs/blob/master/src/web/mod.rs#L316
The bulk of the work was spent in converting the version strings into semver::Version, to sort the array. Something that is already done in CrateDetails...

The original latest_version would return:

• None if req_version was an invalid function or if req_version is the latest version
• Some(version) if this crate has a more recent version

I have split what this function does in two functions:

• CrateDetails::is_latest_version --> check if this is the most recent release
• CrateDetails::latest_version --> grab the most recent release

I like how it is much easier to reason about now 😊

These changes should be easy to follow commit-by-commit. The real changes happen in the second commit: 309ea7a

[jyn514]

Haven't run the code but I have a few initial comments.

[yvrhdn]

@jyn514 I have simplified the code a bit, avoiding the need to call latest_version() twice. Can you take a look again? :)

[jyn514]

Overall I like this :) It will make #396, #312, #223, and #395 easier to fix now that everything's in one place.

#395 would be a good test case for this actually, let me run that locally.

[jyn514]

395 was a separate issue in match_version, it won't be affected.

[yvrhdn]

Overall I like this :) It will make #396, #312, #223, and #395 easier to fix now that everything's in one place.

#395 would be a good test case for this actually, let me run that locally.

About those issues mentioning yanked crates, I have another small-ish refactor coming up which would add a yanked bool to Release. This should make it fairly easy to improve latest_version() and ignore yanked crates.