[RFC] Started initial work on sendMulti

This is just my idea of how the method should look. It should work serially for all adapters and the event system should still be called. Now the trick is to override this method in adapters that support parallel requests...

Feel free to comment or criticize. I am not hung up on this being the way to do it.
Could it be an idea to check all requests before starting any of them? With the current implementation, it could happen that you start some requests, then reach an instance that doesn't implement the desired interface and therefore don't send the following requests. This behaviour seems a bit unpredictable to me.