Use new inner attribute syntax.
Rename crate roots to lib.rs (convention).
Update for Result-yielding Decodable::decode().
Update most `~str` things to `StrBuf`.
Update for struct publicity swap.

(Used to be public by default, private when marked explicitly; now it's
private by default, public when marked explicitly.)
Update rust-phf.
Switch to sfackler/rust-phf (for now).