Allow usage of non-Windows path

[MRigal]

UNIX (Linux and Mac OS) paths is using "/" as separator, unlike Windows which uses "\"

Unfortunately, the R package is using a "fullWinPath" function which does not handle other platform than window. For example, see https://github.com/KWB-R/kwb.abimo/blob/master/R/run_abimo.R#L53

This way, a path input_file <- '/Users/matthieu/dev/kwb.abimo/data/abimo_input_2019.rda' becomes Usersmatthieudevkwb.abimodataabimo_input_2019.rda and it fails...

[MRigal]

FYI, to belong to this point nevertheless the issues pointed in #12, I had to do build the Qt/C++ app locally and faked it as the Windows executable by creating a symlink:
sudo ln -s /Users/matthieu/dev/abimo/src/app/app.app/Contents/MacOS/app /opt/homebrew/lib/R/4.2/site-library/kwb.abimo/extdata/abimo_v3.3.0_win64/Abimo.exe

[hsonne]

With #14 slashes in paths are only converted to backslashes on Windows computers.