Network IDs

[joshuadahlunr]

Create a table of some kind on the GO side, which holds all of the network data structures.
This would then require that on the C side init would need to return an ID for the networking structure created, and every function would need to take an ID. (Also provide _main/_default versions which just pass 0 as the network id.)
On the C++ side, Network could no longer be a singleton!