Add support for Change Streams

[bew]

Doc: https://docs.mongodb.com/manual/changeStreams/

Change streams allow applications to access real-time data changes without the complexity and risk of tailing the oplog. Applications can use change streams to subscribe to all data changes on a collection and immediately react to them.

Note: I think this needs to resolve #29 first, to be able to do other things while waiting for a Change Event.

[bew]

I don't need that anymore, should I leave this issue open?