Redirect short link to latest "public" crate version by default

[Mazwak]

If a crate has a "non public" version (beta, rc, …), the default link points to it.

For example, right now, rust-postgres has 0.15.2 as latest, and 0.16.0-rc1 as test.

http://docs.rs/postgres points to 0.16.0-rc1.
I think it would be better to point to 0.15.2.

Most, if not all, people accessing the default want to read the documentation of the latest "public" version.

[jyn514]

Duplicate of #223