Add WYSIWYG-style markdown editor

[jkaberg]

Would it be possible to add an WYSIWYG toolbar at the top when editing MD files? As one grows older and time passes by one tends to forget syntaxes 😆

I found two examples:

• https://stackedit.io/editor
• https://simplemde.com/

Perhaps make it hideable for people who doesn't want it?

[jmcclelland]

I was about to add the same feature request when I found yours. This would be terrific.

[geek-merlin]

Different but related: #61,