Add Checkbox support

[chrisvasqm]

Checkboxes are not being rendered properly in dev.to, like they do here on GitHub's .md files.

In order to use checkboxes we have to use - [ ] for a unmarked checkbox and - [x] for a marked checkbox

Example:

• Unmarked checkbox
• Marked checkbox

[AnneTheAgile]

@chrisvasqm does github use a public markdown format for its flavor? I love some of its addon's, eg live URL's. Dev.to's markdown is also good. Asciidoc has these things but seems not to have caught on as well? https://github.com/asciidoctor/asciidoctor

//I just came across another parser too that has a plugin structure. RickStrahl/MarkdownMonster#95
I wonder when this repo will be populated?

[TDA]

Ah man, just ran into this today. Are there any alternative ways to get a checkbox to show up? Other than using an emoji lol