-------------------------------------------------------------------------------
   Plots the aircraft data. opt is 'info', 'init', 'store', 'plot'
   If opt is 'info' d is a list of plots. Otherwise it is
   the d returned from ACPlot. The calls are

   d = ACPlot( x, 'init', plots, g, nPts, dT, nSim )

   do k = 1:nSim
     d = ACPlot( x, 'store', d, control )
   end

   ACPlot( x, 'plot', d )

   Possible plots are:

   Altitude
   Euler angles
   Quaternion
   Angular rate
   Position ECI
   Velocity
   Alpha (also get beta and total velocity)
   Mass 
   Inertia 
   CG  
   Engine states
   Actuator states
   Sensor states
   Flex model states
   Disturbance model states


-------------------------------------------------------------------------------
   Form:
   d = ACPlot( x, opt, d, g, nPts, dT, nSim )
-------------------------------------------------------------------------------

   ------
   Inputs
   ------
   x      (:)     Aircraft state vector or 'plot' if opt is 'store'
   opt    (n,:)   Options 'info'
                          'init'
                          'store'
                          'plot'
   d      (:)     Internal data structure or list of plots
   g      (:)     Aircraft data structure or d.control when opt = 'store'
   nPts   (1,1)   Number of plot steps
   dT     (1,1)   Sim time step
   nSim   (1,1)   Number of sim steps
   units  (1,:)   Units
                                  
   -------
   Outputs
   -------
   d      (:)     Internal data structure or list of plots

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