Remove module prefixes from type names

[alexcrichton]

Tracking issue for rust-lang/rfcs#356

[supr]

This also looks like it is not going to be backwards compatible, with the std name changes?

[sfackler]

@supr I believe it can be done backwards compatibly by reexporting the type under the old name.

[alexcrichton]

With all the stability happening recently this has been done.