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   Computes the mass flow divided by the inlet area. The code
   is based on a constant mach number at station 2 which is the exit
   of the diffuser and inlet to the fan or compressor.
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   Form:
   mDot = MassFlow( m0, p0, t0, piDMax, eD, gamma, r, m2, units )
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   ------
   Inputs
   ------
   m0         (1,:)   Inlet mach number
   p0         (1,1)   Inlet pressure
   t0         (1,1)   Inlet temperature
   piDMax     (1,1)   Maximum diffuser pressure ratio
   eD         (1,1)   Diffuser efficiency
   gamma      (1,1)   Rate of specific heats, cP/cV
   r          (1,1)   Gas constant
   m2         (1,1)   Mach number at exit of diffuser
   units      (1,:)   'eng' or 'mks'

   -------
   Outputs
   -------
   mDot       (1,:)   Mass flow

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