BREAKING CHANGE: `createApp` API has been adjusted.
- `createApp()` now accepts the root component, and optionally a props
object to pass to the root component.
- `app.mount()` now accepts a single argument (the root container)
- `app.unmount()` no longer requires arguments.
New behavior looks like the following:
``` js
const app = createApp(RootComponent)
app.mount('#app')
app.unmount()
```
* test: [wip] add tests for rendererChildren
* chore: use serializeInner for clearer output
* fix: should remove the text node if content is empty
* test: also test for appended content
* test: inserting & removing
* test: moving children
* refactor: use a helper function
* test: finish tests
* test: duplicate keys tests belong to keyed children block
* fix(runtime-test): fix insert when moving node in the same parent
* fix: fix failing test cases for rendererChildren
* test: handle rendererChildren edge case
