Add Character Inverse Kinematics for Feet

Add example to project to keep humanoid character feet grounded and locked in place when moving to have animations line up with player movement.

Adding basic foot IK as part of PR #197

Future features left to add:

[x] Add support for layer masks for physics detection of player feets - Added in PR #198
[x] Ensure feet do not overlap with other objects when raised or lowered (force move them to valid positions) - Added in PR #199 - Revised in PR #203
[ ] Have each foot move independently with current moving platform instead of teleporting with player
- [ ] Also have feet rotate with whatever ground they are standing on.
[ ] Not break feet/ankles when no valid ground placement is found.
- [ ] Take a note from zelda and default to placing knee if position is too high up and move foot back.
[ ] If neither foot is placed but player wants to be grounded, search for a location to place feet.
[ ] Add a walking up stairs animation to allow for player to walk up stairs. Tigger when walking up in vertical space.
- [x] revert hip behavior to place height based on lowest grounded foot. - Revised in PR #203
[ ] Account for player hip rotation instead of using the player forward for foot direction.

nicholas-maltbie / OpenKCC