Feature Request: Strikethrough button in toolbar

[rjonesy]

This is semi-related to #12 request for Blockquote button.

My request is to add a strikethrough button to the very nice toolbar you folks have implemented. We use strikethrough often because the first post in an Issue or Discussion is kinda like the overview or progress tracking – so if we decide not to do something we strikethrough it to keep the record.

[rnystrom]

Linking to my comment on checkbox controls.

Strikethrough feels like a good quick-win, we will just need to think about how this bar scales as we add more controls.

[rnystrom]

Landed today and will go out in an upcoming beta!