Simple Newtonian gravity simulator I made a while back

Controls:

• Click to create object, click again to set it off (arrow shows direction and magnitude of velocity)
• Scroll to change mass of object
• G to toggle gravity
• C to toggle collision
• B to toggle a bounding box (at edges of screen)
• Del to delete last placed object
• End to delete all objects

Don't press:

• L locks mouse to centre of screen (rotates screen in 3D mode)
• T 3D debugging mode which does not properly work yet

Todo: Combine this and my 3D renderer to make a proper 3D mode.