FR: Add support for italic formatting

[zx8]

Describe the solution you'd like

Currently, we can do e.g.

[colors]
commit_id = { fg = "green", bg = "#ff1525", bold = true, underline = true }

Would it be possible to add support for italic = true as well?

[arxanas]

Other interesting stylistic options (pulled from https://gist.github.com/fnky/458719343aabd01cfb17a3a4f7296797) might be:

• dim
• inverse
• strikethrough
• blinking

(Not sure which of these we already support, if any? I suppose, in the meantime, you could also manually add ANSI escape codes to your template.)

[martinvonz]

Wikipedia says this about italic ¹:

Not widely supported. Sometimes treated as inverse or blink.

I don't mind still adding support for it. We should probably just not use it in default templates.

Footnotes

1. https://en.wikipedia.org/wiki/ANSI_escape_code#Select_Graphic_Rendition_parameters ↩