Issue #328: include multiple levels of headings in guide TOC

[scottrobertwhittaker]

This is a very short, simple solution to include third-level headers in guides' tables of contents.

[nene]

Nice, but now the issue is at H4 headings.

Some might want to include all H1...H6 to TOC, while others might want just the top level, or maybe even no TOC at all. I have a feeling that it should be configurable.

So I think a better way would be to have a command line option like --guide-toc-level, which would default to H2 like now, but would allow the added flexibility to those who want it.

A third option would be to configure it at the guide level, but I think that would be a rare need.

[nene]

Thanks.

I've pulled this in to a separate branch: https://github.com/senchalabs/jsduck/commits/issue328-guideTOC

Renamed --guide-toc-level to --guides-toc-level, and did some other changes.

[scottrobertwhittaker]

Thanks -- these changes look good, especially your changes to the option documentation.