Implement targeted event sending

[ImmutableOctet]

The idea would be that an event could be received only by the targeted entity. We would do this by filtering to only trigger yield operations of Entity Threads of the targeted entity. This could be achieved using either a MetaAny or a templated wrapper type to hold the event. We could then listen for those targeted events in the Entity System, dispatching accordingly.

This would be useful for messages between entities, and could be extended further to networking concepts like messages to/from a specific player.