if you look the raw content of the erlend-sh you’ll see that is not really markdown but html.
Asciidoc(tor) is reacher than mardown, because it was made for doc and book. The syntax of extension is normalized, so syntax flavor like with markdown.
github (like lot of editor) allow preview, but if you prefer a dedicated editor like MarkdownPad2, you can give a try to Asciidoc Book Editor based on JavaFX 8 (I didn’t try it).