YAML syntax highlighting

Hi!

YAML is a data serialization file format. The problem is that different files can have a YAML header, like .MD files, per example. A header is delimited by three dashes on a line.

The identation of YAML always has to be two spaces.

There's a cheat sheet on the official site. Actually, the home page is written on YAML. The syntax section of the article on Wikipedia is a good start point.

Thank you so much!