Add Redis/RESP input parsing

With this change, we should be able to let redis-cli connect to
a oneshot_protocol server to issue commands and receive responses.

Also, I remembered Erlang has a packet type of `line`, so I simplified
the protocol parsing (removed manual newline detection, derp).

Test added for inbound Redis protocol parsing.

Also add some connection_close notifications so we can die immediately
without lingering.

All tests pass.