ROBUST_CVARS had multiple issues:
* Not composable, i.e. two independent systems can't easily layer CVars to set as they all have to go into one var
* Not sanitary, there's no way to store things that have a ";" in them because it'd always get used as separator.
This adds a new ROBUST_CVAR_* system. For example I can set ROBUST_CVAR_game__hostname=foobar to set a CVar via a single env var. A double underscore ("__") is replaced with a period to make the CVar names safe for environment variables.
Also made Robust.Shared.Configuration.EnvironmentVariables internal because wtf that should not be public no.
Pieter-Jan Briers