- Rename std::io to std::old_io

This is something that I've long wanted to add. It uses libgit2 as an optional dependency.

- uint -> usize
- getopts Cargo library
- replace feature gates with unstable APIs

Also, remove dependency on the Regex library by replacing the one place it was used with standard code that should hopefully be faster anyway.

std::str changes, and the way macros are expanded.

- Prefer iter over into_iter where appropriate
- Cut down on cloning

I'm serious, the more functionality I can use external crates for, the better.

Feels good turning all that code into a dependency!

Yeah, I broke my own code again.