rodrigues_vector_rotation - rotate a 3D vector around another

Rotate vector v around (unit) vector k by theta_rad following the right hand rule.

Vector k will be made a unit vector internally. So its length is irrelevant as long a its greater than 0.

This function is vectorized:
- v can be a 3xN matrix of N vectors that are each rotated around k.
*OR*
- theta_rad can be a vector of N angles.
In either case the output will be 3xN matrix.

Example:
k=[-1;-1;1];
k=k(:)/norm(k);
v=[k(1:2);0];
theta_rads=0:pi/90:(2*pi);
vr = qx.rodrigues_vector_rotation(v,k,theta_rads);
oo=zeros(size(theta_rads));
quiver3(0,0,0,k(1),k(2),k(3),'r','LineWidth',2);
hold on
quiver3(oo,oo,oo,vr(1,:),vr(2,:),vr(3,:));
axis equal
rotate3d('on')

Reference: https://en.wikipedia.org/wiki/Rodrigues%27_rotation_formula

Note: the vectorization for multiple vectors is not a true vectorization, internally a for-loop is used. If you, dear reader, can manage do this without one please let me know how.