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   Euler rates.
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   Form:
   eDot = EulRate( e, w )
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   ------
   Inputs
   ------
   e           (3,1) Euler angles [phi;theta;psi]
   w           (3,1) Angular rates wrt NED [p;q;r]

   -------
   Outputs
   -------
   eDot        (3,1) Euler rates d[phi;theta;psi]/dt

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   Reference: Stevens, B.L., Lewis, F.L. , Aircraft Control and Simulation,
              John Wiley & Sons, 1992, p. 38.
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