Modify polyfit.f
Modify polyfit.f

1. Change polyfit usage to align with other programs.
2. Default output file is polynomial coefficients; optional
   output file is predicted values, i.e. polynomial at
   each x-location of input file.
3. Option to apply constraints on command line or through
   file input.
4. Option to print residual values at each x-location to file.
5. Check for input files.

mherman09/Hdef,mherman09/Hdef,mherman09/Hdef