Refactor docs - move to separate repo, use React and Material UI

[nateplusplus]

There are a few pain points with the documentation site:

1. The documentation for this package has grown significantly in the past year, and it's getting increasingly hard to manage as a series of pug templates.
2. The documentation uses far more dev-dependencies than the actual package build.
3. Bootstrap is not great for a documentation UI.
4. Using a separate github-pages branch was never ideal.

• [ ] Move documentation to a separate repository
• [ ] Refactor everything to React
• [ ] Use Material UI components instead of Bootstrap