Multiple changes:

Reworded & improved comments and POD documentation
Renamed the --frets arg to --max
Built --open & --unplayable logic
Incremented version!
Call --help without any arguments
Repaired fret ranging with separate 0 & max fret
Added horizontal whitespace for double brackets
Renamed setting to just set
Capture setting spec or move on, in loop
Allow --foo=0 with defined foo, instead of ||=
Expand the @spec slice steps for readability sake