Text content templates

Implements a simple mustache-style template parser, allowing binding to individual text nodes.

```html
<ul>
  <li data-each-pass="event.passes">
    <h4>{{ pass.name }}</h4>
    <p>{{ pass.days | number }} day pass</p>
  </li>
</ul>
```

Binding to the element using innerText / textContent is still supported as well through the `text` binder.

```html
<ul>
  <li data-each-pass="event.passes">
    <h4 data-text="pass.name"></h4>
    <p><span data-text="pass.days | number"></span> day pass</p>
  </li>
</ul>
```

Closes #181