This commit adds two backwards compatible changes to prepare for the next Hugo version, most notable:
* All the `File` methods on `Page` has been deprecated and will give a warning in the next Hugo version. Adjust this by changing `.Dir` to ´.File.Dir` and similar.
* Version the capture shortcode to use the old behaviour for markdown rendering of shortcode inner content.
* Reorganize docs contrib guide
* Address first round of feedback from Brad, Jared
* Standardize on 'SIG Docs'
* Address more feedback
* Rewrites to participating.md
* Tweak navigation titles
* Document PR Wrangler
* Document SIG Docs chairperson
* Fix codeblock that shows how to use <codenew>
It was being interpreted as a Hugo shortcode.
Bjørn Erik Pedersen
Luc Perkins
Misty Linville