Return rotational submatrix of a homogeneous transformation
R = t2r(T)
R = T2R(T) is the orthonormal rotation matrix component of homogeneous transformation matrix T.
Works for T in SE(2) or SE(3)
If T is 4x4, then R is 3x3.
If T is 3x3, then R is 2x2.
The validity of rotational part is not checked
For a homogeneous transform sequence returns a rotation matrix sequence