feat: Add or document inverse flag options

[simsrw73]

On Windows, using PowerShell Get-Help with $PAGER configured to use moar, it's cutting of lines when line numbers are displayed. I don't know if that's a bug in moar or PowerShell. PowerShell doesn't give any options for configuring paging at all. Line wrapping option doesn't help at all: words are still cut off. I can add the -no-linenumbers flag to the $MOAR variable to fix it, but then I ran in to the problem of how to show line numbers in other instances. It took me a long time before I blindly stumbled on the solution: -no-linenumbers=f. That's terribly ugly and not documented anywhere that I can see.

Can we have inverted flags for boolean options? -linenumbers or -show-linenumbers? Or at the very least, document how to supply values to boolean flags? This was not obvious to me.