* remove unused `withRule`
* ensure all ::before and ::after elements have content
* update --tw-content for the content plugin
* simplify `before` and `after` variants
* update tests, to reflect changes
* make new `format` and `wrap` API's private for now
* allow returning a format string from `addVariant` callback
* add `content: var(--tw-content)` for before/after variants
* update tests to add `content: var(--tw-content)`
* update changelog
* use String.raw for css escapes
This will allow us to write code like:
```css
.mobile\:font-bold {}
```
Instead of
```css
.mobile\\:font-bold {}
```
Which resembles "real" css way better in our tests.
* use String.raw in integration tests as well
* move `./tests/jit` to `./tests`
* make tests consistent
Abstracted a `run` function and some syntax highlighting helpers for
`html`, `css` and `javascript`.