Use rustfmt to enforce consistent formatting

This change adds a .rustfmt.toml that includes ALL supported settings,
12 of which we have overridden to attempt to cater to our own
proclivities.

rustfmt is checked in the rust-nightly CI job.

src/hpack/mod.rs

@@ -7,6 +7,6 @@ mod table;
 #[cfg(test)]
 mod test;
 
-pub use self::encoder::{Encoder, Encode, EncoderError, EncodeState};
-pub use self::header::Header;
 pub use self::decoder::{Decoder, DecoderError};
+pub use self::encoder::{Encode, EncodeState, Encoder, EncoderError};
+pub use self::header::Header;