Changes to add nav files to documentation

[janet-can]

Rather than try to manage the navigation side-bar using numbers in the headers of docs files, I want to shift to using a nav.yml file in conjunction with a nav.html file. This PR gets us most of the way there, but there are still a couple of adjustments needed.

• Adjust so that folder levels (Get Started, Documentation) expand and collapse when clicked, instead of doing nothing
• Widen the nav sidebar a bit to properly pad the contents and account for longer page titles
• Adjust any CSS to better match the current side-nav actions, styling, and font.

Any comments or feedback welcome! This will be a WAAAY better experience for organizing docs content.

[janet-can]

For reference: http://planetjekyll.github.io/snippets/nav-with-data

[vijaykiran]

You might want to change your editor to add empty new lines at the end of the file :)

[dirkgroenen]

@janet-can I went ahead and resolved some of your "todo" items as per requested in the email. Some changes I made in sodadata/soda-sql@95460d9:

• Use references to pages (page) instead of hard-coded links in your nav.yml. This should prevent any dead links, as well as prevent us from having to go through each link when making a structural change. (We can still support 'absolute links' as well, if you would like).
• Adjusted the rendered template to re-use the template's classes. This gives the look and feel you're looking for.
• Widen up the nav bar a little to make sure all items stay on a single line.
• Toggle the sub-nav when one of its children is active (or when clicking on the array icon)

[dirkgroenen]

Closes sodadata/soda-sql#205

[vijaykiran]

@janet-can I guess this PR on this repo is not needed anymore right ? Since we moved docs to https://github.com/sodadata/docs ?