Add strikethrough to the set of markdown features

[leafcutterant]

I really like the Minimal Markdown Editor for its 1) live rendering, 2) lack of toolbar (screen space, yay!), 3) in-note highlighting.

Strikethrough is not included in its features, but I think it's common and basic enough to make a good case for its inclusion. Therefore I'd like to propose that.

[christianhans]

CodeMirror's GFM mode seems to support this:

https://codemirror.net/mode/gfm/index.html

[moughxyz]

Hmm interesting. Would be nice. A bit preoccupied with the mobile update currently, but if someone wants to tackle this, it would probably be trivial. Take a look at the vim-editor for inspiration. Would probably just be a matter of replacing the vim mode with gfm mode.

https://github.com/sn-extensions/vim-editor/blob/master/index.html#L12