Option for searching for a file on the system path

[madelson]

Some ideas for Windows here: https://stackoverflow.com/questions/3855956/check-if-an-executable-exists-in-the-windows-path/3856090

Not sure how hard it is to make this work cross-platform.

[madelson]

Seems to work on Windows:
https://stackoverflow.com/a/52435685/1142970

[madelson]

Seems like this probably does not work on linux since you need a particular form of exec for that (lp, vp, or vpe): http://man7.org/linux/man-pages/man3/exec.3.html