Sa2Q:

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   Converts an angle vector into a quaternion. 
   Angles are defined as positive rotating frame a into b and the   
   resulting quaternion transforms from frame a to b.

   Since version 1.
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   Form:
   q = Sa2Q( av )
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   Inputs
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   av             (3,1)  Angle vector from a to b

   -------
   Outputs
   -------
   q	            (4,1)  Quaternion from a to b

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