Merge pull request #87 from Ogeon/master

Rust updates, including `fmt::Formatter` and some `&str` -> `StrBuf`
Add support for inserting raw headers
Travis: abandon PPA in favour of official nightly.
Fix up insert_raw so that it compiles.
Merge branch 'header-insert' (#88).
Rust update: ~str and tm_zone in time::Tm are gone