REQ: $version macro for engine discrimination

[MotoLegacy]

Please ensure that your request is predominantly client-based, and not better suited to being logged with the server or mod aspects of QuakeWorld (e.g. mvdsv or ktx)

Is your feature request related to a problem? Please describe.
LibreQuake would like to use configuration files specific to certain sourceports, and to determine the sourceport from within a configuration file we are able to use $version, to at the very least discriminate against FTE. ezQuake appears to not have this functionality.

Describe the solution you'd like
A $version macro, like in FTE, that just returns the string "ezquake" (or similar).

Describe alternatives you've considered
Bad nested hacks. But we can only determine whether it is DP, FTE, or none.

Additional context
N/A

Impact on server or mods
N/A