More convenient ways to handle events

[SOF3]

I'd like to use this in my integration tests. I need to programmatically handle the case where the player receives a message, so that I can check it against expected message. Currently the API only supports packets, which is an unstable API.

There are PocketMine events I can use to handle other stuff like playerinteractevent (and using AwaitStd for the API), but there is no event for receiving messages.