The KeyValues class belongs here. Also reimplemented most loading methods for KeyValues, and adjusted the VPK building code to account for it. Pointers to the engine's implementation of KeyValues have been moved to a separate header ('keyvalues_iface.h'), as this allows external tools code to utilize the standalone KeyValues class implementation. Playlist utilities are completely separated from the KeyValues header; these have nothing to do with KeyValues other than manipulating a global KeyValues object for the playlists, and thus have been named as such and moved to rtech/playlists.
Originally, we store the search results in a CMemory instance which we then assign to the actual function pointer. CMemory is just a pointer class; we can assign the results directly to the actual function pointer. This commit reduces a lot of code verbosity, and also reduced roughly 2KiB worth of static pointers in the resulting executable. This commit also officially deprecates the support for any GameDLL's below S3 (Season 3), since it makes more sense to port the assets from earlier/later games back to the version this SDK supports.
* Changed 'CClient' handle time to 'edict_t' which is an alias of 'uint16_t'.
* Changed 'g_pServerGameDLL' and 'g_pServerGameClients' init (obtain from factory instead).
* Use interface version macro's for obtaining factory pointers instead.
* Added 'g_pServerGameEntities'.
