Add option to use underscores with bold & italic hotkeys

[davecan]

I would be completely fine with that.

Also it turns out at least one other request was previously submitted for this feature:

Markdown formatting: Underscores instead of asterisks with cmd/ctrl+b/i

Is it possible to have the Markdown formatting shortcuts (Bold & Italic) use underscores (_) instead of asterisks (*)? Example: when I press Cmd+B, I’d like bold to look like this: __a bold phrase__, instead of this: **a bold phrase**. Edit: revised the previous sentence to make my request clearer.