code: public Quaternion fromAngleAxis (float angle, float x, float y, float z) {
          float sina = FloatMath.sin(angle / 2f);
          return set(x*sina, y*sina, z*sina, FloatMath.cos(angle / 2f));
      }
docs: Sets this quaternion to the rotation described by the given angle and normalized
  axis.
  
  @return a reference to this quaternion, for chaining.