This should have been done a *long* time ago, back when I initially
added Websocket support. This is the first part of two in improving
loop handler support with regards to socket closure.
Reason may include: {normal, shutdown} for the most normal shutdown,
{normal, timeout} for a loop handler timeout shutdown, or {error, _}
if an error occured.
Now the server defines default headers that can be overwritten by the
handler simply by passing them to the reply/4 function. Default headers
include, for now, Connection and Content-Length headers. Note that it isn't
enough to change the Connection header to close a keep-alive connection
server-side.
