Implement networking subsystem

[rozniak]

In future rzxe will need to support networking - this shouldn't be too difficult, I've written networked applications before and have a fairly good idea on how to draw up some abstractions and whatnot to use in the engine.

Right now this isn't a priority as getting the audio/visual stuff is of course the main focus at the moment. I expect this will be worked on at some point in the future when I resume work on RozWorld as I would like to make it utilise rzxe, and thus networking needs to be present in rzxe.