New "layout tutorial" guide, covering advanced customization topics

[abought]

Purpose

We're trying a new style of topic-guides that cover the connections between features: intended to cover the mid-level in between the existing "per feature" doc pages, and the implementation-focused examples.

TODO

• Editing for clarity and content
• Compare Jekyll vs pandoc renderers to see if we can reduce the build/tooling burden for docs
• Explore moving existing docs to VCS + GitHub pages. The current wiki implementation does not support atomic updates and may be out of date, eg documentation easily falls out of sync with code.
  • Can we improve auto-documentation (via jsdoc, jsonschema, etc)?

[abought]

Tagging @kbruskiewicz as a potential reviewer. We'd like to make sure that this guide covers key topics that are relevant to a power user; feedback and questions welcome.

We're hoping to release milestone 0.11 in the next 1-2 weeks (pending user feedback on the new features), including this guide as a next step in our ongoing docs improvement efforts.

[abought]

Note: some examples could be improved for clarity, eg assoc: assoc ("will this layout work with my data")