Add timeout to cowboy_loop

LH: I have added a test that does both hibernate and timeout
    and fixed a related issue. I also tweaked the docs and tests.

test/handlers/loop_handler_timeout_init_h.erl

@@ -0,0 +1,23 @@
+%% This module implements a loop handler that reads
+%% the request query for a timeout value, then sends
+%% itself a message after 1000ms. It replies a 200 when
+%% the message does not timeout and a 299 otherwise.
+
+-module(loop_handler_timeout_init_h).
+
+-export([init/2]).
+-export([info/3]).
+-export([terminate/3]).
+
+init(Req, _) ->
+	#{timeout := Timeout} = cowboy_req:match_qs([{timeout, int}], Req),
+	erlang:send_after(200, self(), message),
+	{cowboy_loop, Req, undefined, Timeout}.
+
+info(message, Req, State) ->
+	{stop, cowboy_req:reply(200, Req), State};
+info(timeout, Req, State) ->
+	{stop, cowboy_req:reply(<<"299 OK!">>, Req), State}.
+
+terminate(stop, _, _) ->
+	ok.