Replace terminate/2 with terminate/3, adding a Reason

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.

examples/chunked_hello_world/src/toppage_handler.erl

@@ -5,7 +5,7 @@
 
 -export([init/3]).
 -export([handle/2]).
--export([terminate/2]).
+-export([terminate/3]).
 
 init(_Transport, Req, []) ->
 	{ok, Req, undefined}.
@@ -19,5 +19,5 @@ handle(Req, State) ->
 	ok = cowboy_req:chunk("Chunked!\r\n", Req2),
 	{ok, Req2, State}.
 
-terminate(_Req, _State) ->
+terminate(_Reason, _Req, _State) ->
 	ok.