Improvements & Example Levels

Improvements:

- Minimum jump height is ignored when jumping from a wall so you can detach cleaner.

- Sprint now affects acceleration as well as top speed.

- Tweaking of settings to improve overall feel.

- implemented callbacks (on enter, stay, exit etc) so objects can react to when the player collides with them.

- Added example levels to the demo to get a better feeling of what's possible.

- Added fps counter to demo so it's easier to see if controls are being impacted by a performance issue.

- Added cinemachine camera follow rather than a static camera so larger levels can be made.