Rewrite the backend in Rust

[lambda-fairy]

crates.io's backend is written in Rust, and it works quite well. It would be nice if Rustaceans was too, especially as libraries like Hyper and Iron have cropped up in the mean time.

[nrc]

I wouldn't object to this if someone wanted to do it. I'm more of a believer in the right tool for the job rather than 'dogfood all the things', so I'm not super keen, but I'm not particularly tied to the current implementation.

[lambda-fairy]

I've made a start on this here (demo).

It mostly works so far. The missing pieces revolve around search (lfairy/karkinos#5) and keeping the data up-to-date (lfairy/karkinos#4).