Sidenav upgrade

[souperneon]

Also in: https://mapzen.com/common/styleguide/js-components.html#side-navigation

Current behavior:

• Sub-sections are collapsed and are separate pages
• Only one sub-section that is currently active can be open at any given moment

Desired (new) behavior:

• Sub-sections are open on page load
• Sub-sections are one long page instead of multiple pages H1 - Get Started (main sections) H2 - Tangram Basics (page names) H3 - OpenGL (main sections in a page) H4-6 - smaller sections in a page (collapsed, but expandable)

[kkowalsky]

This index.md has the right heading levels.

If you look at the config YML for tangram you'll see that some of the hierarchy can be built in MKDocs, but the index.md doesn't play nice and wants to always be the first part of the TOC (I think)

[kkowalsky]

anything you want to test for the new nav should use the src-tangram-new (Still WIP) folder: https://github.com/mapzen/mapzen-docs-generator/tree/katie/tangram-update

[migurski]

I would split this from the new Tangram work. It's a separate thing that we want apply throughout, and mixing it up with the other new stuff will make it harder to roll out.

[souperneon]

I agree. I was using the Tangram wireframe to illustrate the type hierarchy and explain how the logic should work with the left nav. Once we have a version of it built, testing it with Tangram docs will be good :)

[hanbyul-here]

Leaving a note for future: I spent times with docs-generator, and found out it doesn't know about headers outside of current page context. Page structure from config file is saved as nav, accessible from theme, but headers are not saved as globla object like nav, it is saved in page scope which is only accessible from current page.

[rmglennon]

See also https://github.com/tangrams/tangram-docs/issues/206