Is your feature request related to a problem? Please describe.
As a mod developer, I want an easy way to detect when my client-side-optional or server-side-optional mod is loaded on the opposite side so I can enable enhanced features that use networking.

Describe the solution you'd like
Two entry points - ClientModHandshake and ServerModHandshake that fire when a client connects to a server and both sides have the mod installed. They should provide the version the other side is using, as well as some kind of network connection or player instance to get the network connection from for easy packet sending.