Both Recv::open and Rev::recv_headers check new stream ids against the
previously stream id. The second such check fails.
Now, only Recv::open performs stream id checks.
Fixes#110
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.
