This is primarily a compatibility layer that enables both forward and backward compatibility for all past and future APIs based on the detected running TGS version. It also bundles all it's includes to make future upgrades not have to modify the dme, heck, could even use a submodule if it wanted (not happening). No other changes necessary.
There's an upcoming event system and new chat management functions. Check them out here: https://github.com/tgstation/tgstation-server/blob/303448457e1529c900fa183a8b3c7f2e5459acf1/DMAPI/tgs.dm
Also added /datum/proc/CanProcCall()
Jordan Brown