insert-css, domify, brfs, running example

- use [insert-css](https://github.com/substack/insert-css), in prepend mode
- use [domify](https://github.com/component/domify) instead of hyperglue (no need for hyperglue layer)
- use [brfs](https://github.com/substack/brfs) instead of custom js modules
- make example easier to run
- remove undocumented `opts.insertCss` feature. Since we prepend the css to the DOM,
we are now a true "widget" with easy cascading styling

@substack what do you think?