Add markdown comment characters
Add markdown comment characters

Markdown accepts raw html in most implementations. The `<!-- ... -->` notation makes a comment in html, and so it can make a comment in Markdown as well. 

Both the [language-markdown](https://github.com/burodepeper/language-markdown/blob/master/settings/markdown.cson) package and the base [language-gfm](https://github.com/atom/language-gfm/blob/master/settings/gfm.cson) package implement this.
mpastell/language-weave