v0.0.5: Smooth camera and framerate/physics timestep scaling

The smoothness update! Smoothed camera and smoothed framerates & physics timesteps mean that skateboard handling is now much smoother and more consistent on different machines.

• Added a smooth camera. Camera now tries to follow an imaginary position behind the skateboard, and will less aggressively move towards this position the less far away it is.
• Added framerate and physics timestep scaling. The processing & render time of each frame is now measured robustly, and the physics timestep is adjusted to match the time of each frame (upto a maximum of 1/15th of a second.) In addition, framerate is capped at 60 frames per second.
• Tweaked skateboard acceleration. The board should now respond more quickly. Reason: it's more fun =)
• Added a new example map - 'the big sine'. It's just a big sine wave that you can go very fast on, which exists mostly for testing purposes.

v0.0.4: Physics engine rewrite & camera improvements

• Rewrote physics engine to be much more stable, support rotation, and handle user input
• Slight improvements to camera, including allowing zooming
• New default map (should be more interesting)
• Added FPS output in console

(this is a re-release of v0.0.3, which had an incorrect configuration)

v0.0.2: Initial physics engine

Initial physics engine and one example map. Still a bit buggy. But you can (mostly) roll down a slope now!

v0.0.1: Test of publishing workflow

Check that we can publish to PyPI.