set_color should support equivalent of tput smso (set standout mode)

[krader1961]

The solution for issue #2904 ultimately involved setting and clearing the terminal standout mode with tput smso and tput rmso. It would be nice if we didn't have to shell out to an external command to do something so useful. Whether it's done via pseudo colors (e.g. set_color standout) or adding new flags is TBD.

[floam]

I think that should be a flag as the colors will be modified by it/will persist through it, albeit inverted. Same with tput rev. The set_color interface kind of stinks but I think this is not like "normal" or "reset" in that regard.

--standout makes sense to me. I wouldn't try to think up a cute analogous name for something that is rather this rather specific mode.

[krader1961]

This was implemented by commit b22842a on 2016-12-31 (PR #3650).