feat: unicode mode for icons

[joshka]

In some contexts the nerdfonts are not easily available (e.g. when pasting a copy of the tree into some documentation).

I'd like a mode that just uses standard unicode characters for icons rather than nerd fonts. This will look very bare in comparison to the default, but will also be easy to copy paste without showing unicode placeholder characters. These icons seem to be the characters available that work in most fonts

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[cafkafk]

You could technically theme your way out of this now, but it would still be useful perhaps... a lot of work to keep and maintain two icon sets thou

[joshka]

Ironically the document icons don't appear on iOS at all (at least in the font that GitHub uses there, which is a bit of a pain. I think on that basis perhaps it's perhaps worth not doing this.

Pasting for non mono space font check.

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Edit: also bad :/