Zircon Beta engine source 20240427 WIP file

Largely completed source code for a future release. Amongst changes: "SMEJ2" single player startup fix resolving sometimes "solid cobwebs". Detection/handling of CTRL + "+" on Italian keyboards. CodeBlocks project for Linux (CodeBlocks is open source IDE). Clears re-entrant menus on gamedir change. TrueType font support from memory. Gamedir change cvar reset is rock-solid now. Large reduction of the number of pragma message developer messages when building engine. And other changes in readme.