Add shortcode support for alternate font (specifically a fixed pitch font)

[instancezero]

It would be useful to have a shortcode for switching to an alternate font. In my use case, this would be a fixed pitch font to indicate machine-generated text, but the solution might benefit from a more general implementation.

Ideas for implementation:

• this is regular text [fixed]this is fixed pitch[/fixed] and back to regular
• this is regular text [alt]this is fixed pitch[/alt] and back to regular

[locrianz]

I would love this as a quick way to switch to and from a font that blacks out what I'm writing, so I can just write and not get caught up in my editing brain.

[vkbo]

I would love this as a quick way to switch to and from a font that blacks out what I'm writing, so I can just write and not get caught up in my editing brain.

I think #1721 would be more suitable for that,