Improved limit()/clamp() behaviour - now it doesn't call nor(), reusing the
(needed anyway) len var, resulting in *one* scl() call instead of *two*.
Also, we use cached len, so that we don't have to calculate it twice.
Mostly beneficial for Vector3 class.
Also adds limit2(),setLength(), setLength2() and removes docs inherited
from Vector interface
Merge pull request #2544 from vaxquis/master

Improved limit()/clamp() behaviour - now it doesn't call nor(), reusing ...