Tools3d: Moved length() method to Vector3d

... and use Math.hypot() instead of Math.sqrt() to prevent underflows and
overflows
Tools3d: Moved scaleBy() method to Vector3d
Tools3d: Moved scaleToLength() and makeUnit() methods to Vector3d
Vector3d: Return this from modification methods to allow chaining
Tools3d: Moved add() method to Vector3d and added set() method
Tools3d: Moved subtract() method to Vector3d
Tools3d: Replaced clone() method with Vector3d.set()
Vector3d: Return this from subtract() method
Vector3d: Added subtracted() method
Cloud: Simplified setCorners() method
FlyingBody: Simplified rotateBody() method
FlyingDot: Simplified avoidHills() method
FlyingDot: Simplified avoidHills() and setLocalFrame() methods