asciidoc: better rendering of table of content (ToC)

Summary

Support for rendering the ToC is not complete. These are the items missing as far as i encountered them so far

• the ToC's title has no css header and hence is rendered as a normal paragraph text
• :toc: left/right placements are not supported

This should be either fixed or documentend, the latter i have done now via this ticket. Not sure if this is bug or feature....