feat(headers): adds re-parsing ability when getting typed headers

BREAKING CHANGE: added requirement that all HeaderFormat implementations
  must also be fmt::Debug. This likely as easy as slapping
  #[derive(Debug)] on to any custom headers.

Cargo.toml

@@ -19,5 +19,4 @@ openssl = "*"
 rustc-serialize = "*"
 time = "*"
 unicase = "*"
-unsafe-any = "*"
 url = "*"