Asciidoc Syntax Highlighting

[buko]

Since syntax highlighting for Markdown was recently added (#291 ) I thought I would also put up a vote for adding highlighting for asciidoc. I've actually seen several projects move from markdown to asciidoc because asciidoc is superior and more standardized than Markdown.

The full asciidoc syntax may be too complicated but even supporting the syntax from the quickstart would go a long way.

[bobbylight]

I just moved to a new state and thus unfortunately haven't had enough tine to give love to this project lately, so pull requests are definitely welcome! I'll consider this when I have time though,