Opt-out of old-school windows ENV flags

[codefromthecrypt]

Checklist

• [x] Are you running the latest v2 release? The list of releases is here.
• [x] Did you check the manual for your release? The v2 manual is here
• [x] Did you perform a search about this feature? Here's the Github guide about searching.

What problem does this solve?

Env variables like %FOO% are old-school, like cmd.exe. Those using powershell will use normal env conventions like $FOO. Right now, the prefix/suffic logic is hard-coded based on runtime.GOOS and can't be easily overridden.

Solution description

Assuming some want the %FOO%, a global flag to undo it without having to override the entire stringer function.

Describe alternatives you've considered

I've tried string replacement to undo this with a wrapped stringer function. Another option is to let it slide, but I prefer the help/markdown to be in powershell syntax.