rustdoc: put unqualified item name first in titles

[jsha]

When you have a lot of tabs open, the Rust stdlib documentation starts to look like this:

I think we should put the unqualified item name first. So for instance:

Vec in std::vec - Rust

String in std::string - Rust

Read in std::io - Rust

This would make finding the right tab in a busy browser easier.

[syvb]

@rustbot claim