AU2Q:

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   Convert an angle and a unit vector to a quaternion.
   Transforms from the unrotated to the rotated frame.

   Since version 2.
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   Form:
   q = AU2Q( angle, u )
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   Inputs
   ------
   angle         (1,:)   Angle (rad)
   u             (3,1)   Unit vector

   -------
   Outputs
   -------
   q             (4,:)   Quaternion from unrotated to rotated frame

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