`text` doesn't encode the string

```dart
final document = html(
  c: [
    div(c: [text('<p>title<strong>asdf</strong></p>')])
  ],
);
```
expected:
```html
<div>
    &lt;p&gt;title&lt;strong&gt;asdf&lt;/strong&gt;&lt;/p&gt;
</div>
```

actual:
```html
<div>
    <p>title<strong>asdf</strong></p>
</div>
```

however this acts as a useful workaround for #14 