Add feature to show checkboxes or tasklists as in GitHub

[dtchanpura]

GitHub markdown supports creation of checkboxes by writing [ ] (space inside square brackets) and selected checkbox by [x] (x inside square brackets)

Just like as follows

- [ ] not selected
- [x] selected

Reference: https://blog.github.com/2014-04-28-task-lists-in-all-markdown-documents/

[theBusterben]

i totally support this feature to be added, i use it all the time for taking notes. I still have to type this to make it appear though

<ul>
<li><input type="checkbox" disabled> foo</li>
<li><input type="checkbox" disabled checked> bar</li>
<li><input type="checkbox" disabled> baz</li>
</ul>

If this feature is going to be implemented, i would also like to suggest crossing off the checkbox to be made also possible in the preview window

[fabiocolacio]

I agree that this is a nice feature to add. We use scidown, as a markdown parser, so you might consider opening this issue there also, but I may implement this myself if I can find the time.

[smithfred]

Would be better to support the full set of GFM extensions if possible, since it's a widely used set of extensions (and is fully specified against CommonMark).

[stefs]

Here is the relevant scidown issue: https://github.com/Mandarancio/scidown/issues/7 However scidown seems to be unmaintained/abandoned. The last released version is 4 years old. Maybe it is better to switch to a different parser because of this.