This PR adds `max_concurrent_streams()` methods to the client and server `Builder`s to set the `max_concurrent_streams` setting. I've added unit tests to ensure the correct SETTINGS frame is sent.
Closes#106
The Connection type is a `Future` that drives all of the IO of the
client connection.
The Client type is separate, and is used to send requests into the
connection.
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
