THE MACHINE ROOMS stage is complete!

A major step towards the completion of the whole game has just been made. Plus a few other little improvements.
Also, the final decision has been made: the full game will be free!

CHANGELOG

• Added THE MACHINE ROOMS stage.
• Touched up graphics of the other stages.
• Touched up a couple of arenas.
• Improved walls tiles selection logic.
• Fixed handling of vertical doors shadows.