add layercake components, stories and docs

[rachelmarconi]

What's in this pull request

• New component/feature

Description

Adding Layercake axes components according to what was used in the medical debt project.

NOTE: the axis components have since been updated on Layercake, so we can update further or not. Some of the new parameters could be very useful. New AxisX. New AxisY.

TODO:

• add code chunks for css if updating manually

Before submitting, please check that you've

• Formatted your code correctly (i.e., prettier cleaned it up)
• Documented any new components or features
• Added any changes in this PR to the CHANGELOG.md Next section
• If this pull request includes a new component or feature, has it been exported from one of the library's entry points?
• Does the component dispatch relevant interaction events? (ie: on:click, on:change, etc.)
• Does the component directory include description and usage information in .stories.svelte?

[mitchthorson]

This is looking really good! I left a few organizational comments and a few nitty-gritty technical comments. Let me know if you want to talk through any of the details here!

[mitchthorson]

Ok just one tiny last suggestion: to have the "Intro" page listed at the top of the Layercake section, just add one additional line below "Layercake" here:

...
"Layercake",
 ["Intro"],
...

Which should result in this ordering: