Detects shell and returns full path on windows

[matthewdeanmartin]

tested with powershell, gitbash, cygwin, mingw.

The one pytest still passes, I didn't see any other checks to run.

Launching these shells by just invoking the full path is still going to be hit or miss, for example launching git bash requires

"C:\Program Files\Git\usr\bin\bash.exe" --login

and of course these are all backslash format & different shells have different strategies for handling full paths.

[uranusjr]

🚢

[TBBle]

The README should probably be updated to remove the note about Windows only returning the shell executable name, without a path or extension.

[uranusjr]

PRs are always welcomed!