Extend rustdoc search

[GuillaumeGomez]

First idea

It'd be nice to write stuff like: "avec"::Vec or even vec::.

In the first example, you look specifically into the "avec" module/type and look for "Vec" inside it.

In the second example, you just look at everything inside the matching "vec" parent (so that maybe return a lot of things with a bad order).

Of course, both features could be used at the same time like: hello::"avec"::.

Second idea

Another idea that came out was to be able to look at functions based on their arguments.

Third idea

Having reverse search: instead of looking for something, you'd look for anything that isn't this thing. However, it wouldn't be on the text search itself but on the items filtering. For example: "!struct:Vec".

cc @rust-lang/rustdoc