Project: webpack
Task (moderate): Supporting importing frontmatter from markdown files.

For example:

hello.md
```md
---
author: hello
tags:
  - foo
  - bar
---

## Markdown Heading
```

index.js
```js
import md, { frontmatter } from './hello.md'

frontmatter.author // should be "hello"
frontmatter.tags // should be ["foo", "bar"]
```

Besides this
- Update `import md from './hello.md'` to `import md, { frontmatter } from './hello.md'` in `src/index.js`.
- Display `frontmatter.author` in div element in `src/index.js`