Update and stabilize SemVer

http://discuss.rust-lang.org/t/stabilizing-semver/376/18 got a lot of discussion, but kinda died out.

What do you think?
I don't necessarily agree with the premises in that you should *certainly* use an int/uint for computations. If they're not useful then why do we have them in the language? The whole point of an "int" is that it's the *default integer*. If we recommend *not* using the default, then why do we use the default in the first place?

I also don't agree that `u32` is significantly faster than `u64` in an application such as this. We're not calculating semver comparisons millions of times in a tight loop, so any benefit of a 32-bit integer over a 64-bit one is completely lost in the noise of other application logic.

There's not a strong precedent in the existing libraries to take `u32` *instead* of `uint`, and I'm a little wary to start that trend without a lot of data. If `uint` defaults to the wrong integer size, then that needs to be fixed in the rust language, not all the libraries.