Added fall damage detection module

[Malcolmnixon]

This pull request implements feature #144 for fall detection. The implementation works by detecting instantaneous accelerations above a given threshold. There are options for:

• Suppress acceleration/damage caused by the player being launched into the air - for example by jump pads
• Detect only damage caused by colliding with the ground, as opposed to colliding with a wall

[BastiaanOlij]

Hmmm, I'm not sure about this one, it's a bit strange implementing specific game logic into a generic toolkit. I need to think about this and whether there is a more generic approach, this has the danger of implementing all sorts of specifics as people want to detect other forms of impacts.

[Malcolmnixon]

I moved the fall-detector into an "examples" folder and put an extensive comment explaining that it was an example and that games would most likely need to customize it.