Callback support for send methods

[mdnorman]

Hey! This is a good library. I'd love to start using it for some projects.

I noticed that the send-only methods (eg setBlock) don't take in a callback. This means I can't be sure when that's been done before closing the connection or completing other work.

I'm happy to help code those in, but I noticed in a comment on the previous issue that you're working on a new version and didn't want to step on your toes. I'll probably start coding them in a fork soon.

[mdnorman]

I decided to fork the minecraft-pi-promise instead to just use the promise support.