MADS: Merge of Rex Nebular game engine

This is a request for merging the MADS engine into master. As Strangerke so eloquently put in his blog posting, all the hard-coded scene logic for the game is done, and we have a fairly solid core engine. The only functionality still missing is original game dialogs (such as save, load, options) and the original starting menu and associated options (the credits, intro sequence, etc.). There are also still some very minor bugs to fix, and likely more will come up and be fixed as we test our way through the game.