netcore provides the main binary file, the network server, a library loader, and a NetServer object that abstracts networking into events.
It dynamically loads mudlib, and asks it to run its main loop, giving it a mutable referene to the NetServer for it to receive and send network events.
The mudlib's main loop can request to be restarted, giving netcore an opaque object; netcore will unload the library, load a new version, and give it the opaque object.
The mudlib uses this to send a bincode-serialized Connections object, in order to remember about the state of open connections, players attached to each connection, and their telnet negotation state.