Support italic style in printstyled.

[fredrikekre]

No description provided.

[vtjnash]

We did not include this because it does not reliably make it italic, except on monochrome monitors. On color monitors, it may invert the colorscheme instead:

macOS Terminal running tmux:

macOS Terminal not running tmux:

https://en.wikipedia.org/wiki/ANSI_escape_code#SGR_(Select_Graphic_Rendition)_parameters

[vtjnash]

Note that even this support might be quite recent, since people were writing blogs about it not working within the past few years: https://weibeld.net/terminals-and-shells/italics.html

[fredrikekre]

Rebased. I included a note about terminal support in the docstring.

[tecosaur]

It's worth noting (and I think short of the docs a comment here has a chance of being seen at least) that italic support can be checked for in terminfo, and so the best practice would be adapting the printing behavior based on the terminal capabilities.