Show latest non-yanked version (if any)

[SimonSapin]

/crates/<name> (without a version number) should show the latest version of the crate that is not yanked (if any).

For example:

• The latest publish version of url was 0.2.37
• A number of changes were merged in the git repo since, including one breaking change
• I published 0.3.0
• Then I realized that the breaking change was incorrect. I reverted the commit, and ran cargo yank --vers 0.3.0
• I published 0.2.38 for the other changes

Now https://crates.io/crates/url shows 0.3.0 with "This crate has been yanked". It should show 0.2.28 instead.

[alexcrichton]

I believe this is a dupe of #76, so closing in favor of that.

[SimonSapin]

Ah, I didn't realise that max_version was what I was looking for. Sorry for the duplicate!