Allow passing options to sub protocols

Before this commit we had an issue where configuring a
Websocket connection was simply not possible without
doing magic, adding callbacks or extra return values.
The init/2 function only allowed setting hibernate
and timeout options.

After this commit, when switching to a different
type of handler you can either return

  {module, Req, State}

or

  {module, Req, State, Opts}

where Opts is any value (as far as the sub protocol
interface is concerned) and is ultimately checked
by the custom handlers.

A large protocol like Websocket would accept only
a map there, with many different options, while a
small interface like loop handlers would allow
passing hibernate and nothing else.

For Websocket, hibernate must be set from the
websocket_init/1 callback, because init/2 executes
in a separate process.

Sub protocols now have two callbacks: one with the
Opts value, one without.

The loop handler code was largely reworked and
simplified. It does not need to manage a timeout
or read from the socket anymore, it's the job of
the protocol code. A lot of unnecessary stuff was
therefore removed.

Websocket compression must now be enabled from
the handler options instead of per listener. This
means that a project can have two separate Websocket
handlers with different options. Compression is
still disabled by default, and the idle_timeout
value was changed from inifnity to 60000 (60 seconds),
as that's safer and is also a good value for mobile
devices.

doc/src/manual/cowboy_loop.asciidoc

@@ -29,8 +29,6 @@ Loop handlers implement the following interface:
 init(Req, State)
     -> {cowboy_loop, Req, State}
      | {cowboy_loop, Req, State, hibernate}
-     | {cowboy_loop, Req, State, timeout()}
-     | {cowboy_loop, Req, State, timeout(), hibernate}
 
 info(Info, Req, State)
     -> {ok, Req, State}
@@ -42,7 +40,7 @@ terminate(Reason, Req, State) -> ok  %% optional
 Req    :: cowboy_req:req()
 State  :: any()
 Info   :: any()
-Reason :: stop | timeout
+Reason :: stop
         | {crash, error | exit | throw, any()}
 ----
 
@@ -65,37 +63,15 @@ stop::
     The handler requested to close the connection by returning
     a `stop` tuple.
 
-timeout::
-    The connection has been closed due to inactivity. The timeout
-    value can be configured from `init/2`. The response sent when
-    this happens is a `204 No Content`.
-
 {crash, Class, Reason}::
     A crash occurred in the handler. `Class` and `Reason` can be
     used to obtain more information about the crash. The function
     `erlang:get_stacktrace/0` can also be called to obtain the
     stacktrace of the process when the crash occurred.
 
-//{error, overflow}::
-//    The connection is being closed and the process terminated
-//    because the buffer Cowboy uses to keep data sent by the
-//    client has reached its maximum. The buffer size can be
-//    configured through the environment value `loop_max_buffer`
-//    and defaults to 5000 bytes.
-//    +
-//    If the long running request comes with a body it is recommended
-//    to process this body before switching to the loop sub protocol.
-//
-//{error, closed}::
-//    The socket has been closed brutally without a close frame being
-//    received first.
-//
-//{error, Reason}::
-//    A socket error ocurred.
-
 == Changelog
 
-* *2.0*: Cowboy temporarily no longer checks the socket for data with HTTP/1.1.
+* *2.0*: Loop handlers no longer need to handle overflow/timeouts.
 * *1.0*: Behavior introduced.
 
 == See also