Support other POSIX-copliant OSs

[fancsali]

The disfetch tool itself being written in POSIX shell, it seems to be an obvious stop.

A few pop to mind, mainly *BSD variants, and – God forbid – MacOS/Darwin.

[q60]

i guess i will be able to get back on track w/ disfetch soon. expect changes in november. sorry for not maintaining it :/

[q60]

i really struggle with other *nix OS cuz no QA