Add max_frame_size option for websocket handlers

Option allows to limit a frame by size before decoding its payload.

LH: I have added a test for when the limit is reached on a nofin
fragmented frame (the last commit addressed that case but it had
no test). I have fixed formatting and other, and changed the
default value to infinity since it might otherwise be incompatible
with existing code. I also added documentation and a bunch of other
minor changes.

test/ws_SUITE_data/ws_max_frame_size.erl

@@ -0,0 +1,22 @@
+-module(ws_max_frame_size).
+
+-export([init/2]).
+-export([websocket_init/1]).
+-export([websocket_handle/2]).
+-export([websocket_info/2]).
+
+init(Req, State) ->
+	{cowboy_websocket, Req, State, #{max_frame_size => 8}}.
+
+websocket_init(State) ->
+	{ok, State}.
+
+websocket_handle({text, Data}, State) ->
+	{reply, {text, Data}, State};
+websocket_handle({binary, Data}, State) ->
+	{reply, {binary, Data}, State};
+websocket_handle(_Frame, State) ->
+	{ok, State}.
+
+websocket_info(_Info, State) ->
+	{ok, State}.