* Added math equations to Quaternion, Vector and Matrix method
documentation.
* Removed confusing Quat*=Quat operator overload, as it isn't exactly
clear from which side the non-commutative multiplication is done:
Quaternion a;
a *= b; // eh?
a = a*b; // okay!
For similar reason this operator wasn't present in RectangularMatrix
either.
* Unified documentation of expected vector/quaternion normalization
state. Now it is not "assumed" but "expected", because failing to do
so results in assertion failure.