Support for socketed linking

It'd be nice if, on standard builds (i.e., not libretro), SameBoy would be able to transmit link cable data to and from a socket (completely raw, not compressed or anything) on the local machine. This would make various things possible that wouldn't be possible without rebuilding SameBoy.

For instance, I had an idea for hooking up Pokemon Red to Pokemon Showdown (for the sake of novelty). Without this feature, it wouldn't be possible unless I went through the SameBoy code and modified the link cable code, and injected custom code in to: A. Parse the link cable data B. Connect to Pokemon Showdown's servers C. Act as a Pokemon Showdown client

This would obviously pose a challenge, because throwing all this into a custom build of SameBoy would be incredibly hard, which is why this would come in handy.