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.

Also link from the guide to manual pages.

The old interface with ok|reply|stop tuples is deprecated.

This required moving around a lot of things so hopefully I
did not add errors while doing so. Only time will tell.

Also add the 415 that can result from content_types_accepted.

When the method is PUT we do not check the location header.