Thread to handle one client request. Gets the request from the client and
sends the response back to the client.
The server responds to some header settings:
X-ResponseStatus - the response code/message; default "200 OK"
X-SetHeaders - pipe-separated list of headers to return
X-ResponseLength - truncates the response to the stated length
X-SetCookie - set a cookie
X-Sleep - sleep before returning
It also responds to some query strings:
status=nnn Message (overrides X-ResponseStatus)
redirect=location - sends a temporary redirect
v - verbose, i.e. print some details to stdout