An vector of orientations, each represented by a vector of numbers.
Each of these types stores orientations as rows of a matrix in slot x.
The eulerzyx class uses 3 Euler angles in the roll-pitch-yaw scheme
(rotation about Z axis, then Y axis, then X axis).
The eulerzxz class uses 3 Euler angles in the X system scheme
(rotation about Z axis, then X axis, then Z axis again).
The rotvector class uses the 9 components of a 3 x 3 rotation matrix, stored
in column-major order.
The quaternion class uses the 4 components of a unit quaternion.
The skewvector class uses the 3 non-zero components of a skew-symmetric matrix,
where (x,y,z) stores the matrix ((0, -z, y), (z, 0, -x), (-y, x, 0)).