Forward C model not cross compatible with non Linux OS

[gabe-parrish]

The forward model in C breaks down when run on a non-Linux OS.

Also, the C code will break if the parameter file contains an empty 'Cooling File' parameter which is a default parameter when saving the forward model results so this may cause an error for users not aware that they would have to remove 'Cooling File' line from the parameter .txt file for the inverse solver to work properly.