* Add support for React components.
This adds support for react components via a new `extensions` config in astro.config.mjs. In the future we can extend this to do things like look at the import statements, as Snowpack does.
* Fix the tests
* Initial tests set up
This adds tests using uvu (we can switch if people want) and restructures things a bit so that it's easier to test.
Like in snowpack you set up a little project. In our tests you can say:
```js
const result = await runtime.load('/blog/hello-world')
```
And analyze the result. I included a `test-helpers.js` which has a function that will turn HTML into a cheerio instance, for inspecting the result HTML.
* Bring snowpack example in
* Formatting
