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.
This adds a `Codec` based testing API. This is a bit less annoying than writing at the raw H2 wire protocol level...
Codec
Exposes `Codec` using an unstable flag. This is useful for testing.