Added rotate_vector and some constructor functions
Added rotate_vector and some constructor functions

'rotate_vector' rotates a given Vector3 with the given quaternion.

'quaternion_from_euler_angles' constructs a unit quaternion for the given
euler angle rotations (in radians)

'quaternion_from_axis_angle' constructs a unit quaternion for the given
unit rotation axis and angle (in radians)

PistonDevelopers/quaternion,bvssvni/quaternion,stjahns/quaternion