Improved implementation and unit test for Vector3.angleTo to account for numerical problems outside of full [-1,1] range.

Fixed bug in Vector3.angleTo where NaN was being returned instead of zero. Added corresponding unit test.

remove Vector3.projectOnUnit, add Vector3.projectOnPlane (equivalent to previously removed orthoTo).

Removed Vector* add() to addVectors() and addSelf() to add(). Same with sub, cross, min, max, lerp... Renamed Matrix* and Quaternion multiply() to multiplyMatrices(), multiplyQuaternions() and multiplySelf() to multiply(). See #2860.
Good thing we have a ton of examples to make sure nothing is broken. The unit tests also helped. However, I suspect I've left something unchanged.

inline Vector2/3/4/Quaternion.length()/lengthSq() and optimize Vector2/3/4.setLength() with unit test coverage.

implemented Box3.transform, tested.  Removed Box3/Box3.scale as it doesn't work in the general case.  move tests to tests/math from tests/core to replace move of tested source files.

add Triangle3, add optionalTargets to Box2,Box3,Plane,Sphere,Ray where possible to reduce GC load, add Triangle3 unit tests.

Vector2: setX, setY, Vector4: setX, setY, setZ, equals.  Unit tests for Vector2, Vector3 and Vector4.