Highlight "setext-style" headers (-- and ==)

[vjpr]

My headers using atx-style appear blue.

But when using settext-style (https://daringfireball.net/projects/markdown/syntax#header) they are not.

[burodepeper]

I'm aware of this issue. The simple answer: the way Atom allows to parse content doesn't allow the detection of new lines in a pattern, which is needed to detect setext-style headers. See the FAQ on this. Unless the way grammars work are fundamentally changed, setext headers simply can't be implemented.

[73]

The language-gfm Issue is still open as well...