Allow the wavelength scale to be fixed within grand

[bjfultn]

Try CPS wavelength solution as initial guess to address behaviors seen in issue #18

[bjfultn]

Actually, I'm not sure if I know how to do this. I thought it would be as easy as replacing the hires.wave file with a CPS version, but I don't think the fortran code reads in that IDL save file. @JayVB where does grand get it's initial guess for the wavelength solution?

[JeffValenti]

@JayVB and I just discussed this issue. Currently, the initial wavelength guess is hard-coded in grand.F. Jay will:

• Modify grand.F to read the initial wavelength specification from a disk file.
• Add a command line option to specify the input wavelength file. If not specified, grand will read a default wavelength file from the fortran reference file directory.
• Add a command line switch that suppresses refinement of the wavelength solution. In this case, the input wavelength solution would be used throughout the calculation.
• Modify grand.F to write the final wavelength specification to disk. This will allow iGrand to propagate the same wavelength scale through subsequent iterations of grand.

[bjfultn]

@JayVB has implemented this feature in grand. Tests have been run and we verified that it is working as expected.