Linux support

[Huite]

These are some mostly cosmetic changes to get it compiling on Linux.

I've added a basic test case, which runs on Windows (with the original exe, and the one I've built myself).
Unfortunately, the Linux executable doesn't run properly yet. Adding a print statement tells me that it does run; I can print the command line argument, but it seems to be hanging afterwards.

Easiest is to start a debugger and see where it's going awry. VSCode can connect to gdb running in WSL, with a little bit of setup. I should document this.

I have relatively good hopes that if we get this working for Linux, that it'll probably also work for Mac.

[Huite]

I suspect this line is causing problems, in line 2508 gfio.for:

      OPEN(ILUNEW,ERR=6500,FILE=AFILE,STATUS='OLD')

The value here of AFILE is: 'WELL_UFLOW.DAT '

While the argument in the command line is well_uflow.dat.

On Windows, this won't generate a problem because lower/upper case doesn't matter.
However, I guess on Linux, this tries to read a file that doesn't exist.

Interestingly, I can get it run fairly successfully when I copy the file to a new name WELL_UFLOW.DAT.
I say fairly succesfully, because it appears to echoing to stdout, while no ECHO directive is provided in the .dat file.