Add "both" mode that highlights foreground and background

[harrygallagher4]

I had a very specific use case (printing a gradient) that made the high-contrast text get in the way so I hacked together this extra mode and thought some others might like it. I couldn't think of a better abbreviation than "mbf" since "mb" is already taken, I'm not sure how much the abbreviation matters to you but maybe you can think of a better one or a better name than "both." Anyway, thanks for this plugin :)

(sorry about the @ 2x images, i'm not sure why they weren't resized properly)