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   Computes the required roll distance and liftoff velocity.
   To see a demo, run with no inputs:  [s,v,def] = Takeoff;
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   Form:
   [sTotal, vLiftoff, def] = Takeoff( d, altitude )
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   ------
   Inputs
   ------
   d              (1,1)  See "ConcordeProperties.m"
   altitude       (1,1)  Altitude (m)

   -------
   Outputs
   -------
   sTotal         (1,1)  Ground roll (m)
   vLiftoff       (1,1)  Liftoff velocity (m/s)
   def            {12,3} Data structure definition

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