host: strip `.exe` for greatfet subcommands
host: strip `.exe` for greatfet subcommands

Also hides the `-script.py` file for each command, since Windows puts
those in the PATH as well.

Fixes #243

dominicgs/GreatFET-experimental,greatscottgadgets/greatfet,dominicgs/GreatFET-experimental,greatscottgadgets/greatfet,greatscottgadgets/greatfet,greatscottgadgets/greatfet,dominicgs/GreatFET-experimental