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   Compute the burnout velocity for a multi-stage rocket
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   Form:
   [vBO,dV,tOF] = BurnoutVelocity( d );
     -or-
   [vBO,dV,tOF] = BurnoutVelocity( mPLD, mSS, sR, Isp, thrust );
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   ------
   Inputs
   ------
   d            (.)    Data structure with fields
                 .mPLD    (1,1)    Mass of payload (kg)
                 .mSS     (1,N)    Mass of structure for each stage (kg)
                 .sR      (1,N)    Structural mass ratio for each stage
                 .Isp     (1,N)    Specific impulse for each stage (sec)
                 .thrust  (1,N)    Thrust for each stage (kN)

     -or-

   mPLD        (1,1)   Mass of payload (kg)
   mSS         (1,N)   Mass of structure for each stage (kg)
   sR          (1,N)   Structural mass ratio for each stage
   Isp         (1,N)   Specific impulse for each stage (sec)
   thrust      (1,N)   Thrust for each stage (kN)
                       

   -------
   Outputs
   -------
   vBO         (1,1)  Burnout velocity [km/s]
   dV          (1,N)  Delta-v for each stage [km/s]
   tOF         (1,N)  Time of flight for each stage [sec]

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