This allows changing the normal exit reason of Websocket
processes, providing a way to signal other processes of
why the exit occurred.

We now stop reading from the socket unless asked to,
when we reach the request body. The option
initial_stream_flow_size controls how much data
we read without being asked, as an optimization.
We may also have received additional data along
with the request headers.

This commit also reworks the timeout handling for HTTP/1.1
because the stray timeout message was easily reproducible
after implementing the flow control. The issue should be
gone for good this time.

Better than sending messages manually.