Document that toString() is performed on the message argument
Document that toString() is performed on the message argument

This is what engine.io in fact already (implicitly) does, so I can give it any object I want, and it will send what `message.toString()` returns.

This allows me to implement transparent caching of the JSONified string, speeding up broadcast and multicast messages.
nkzawa/engine.io,socketio/engine.io,socketio/engine.io,CantemoInternal/engine.io,kapouer/engine.io