Add crates.io!

[carols10cents]

@alexcrichton sayyyyys we cannnnnn

crates.io's code builds on stable and I have no plans to change that for the foreseeable future

I also test on beta and nightly; this issue is prompted because I started seeing beta be over travis' memory limit - rust-lang/rust#43789

[Mark-Simulacrum]

This change has deployed and the collection has started.