1.01.13: Red/blue 3D glasses mode

There is a new 3D red/blue glasses mode. The user can customize the distance between the player's eyes and the appearance of the HUD.

Changed menus that require the inputting of a number to be more friendly by having slider bars. This makes the game easier to customize while using a controller. Also made other parts of the GUI easier to use with a controller.

Updated the engine to use more modern OpenGL functions.