Add support for converting the TOC to raw markdown

[DanteDeRuwe]

Is your feature request related to a problem? Please describe. I really like the [TOC] feature. Most of my markdown is however meant for use on GitHub, and there, the raw text "[TOC]" is displayed. I always have to copy-paste my entire markdown into an online tool (like this one) to generate a markdown TOC.

Describe the solution you'd like A button or shortcut to insert an actual raw markdown TOC

Describe alternatives you've considered

1. When linking to github, the conversion of [TOC] to actual markdown (not ideal)
2. a button or right click menu action to convert the [TOC] tag into actual markdown (more ideal)

[bebeisdog]

I also have this problem and idea. I wonder if Hackmd has solved it now or has any ideas? :)