Html5 custom data attributes in tag helpers

You can use Html5 custom data attributes in your templates. For example:
```perl
  %= text_field foo => 1, data => {id => 1, name => 'ok'}
```
and you'll get a markup like this
```html
<input data-id="1" data-name="ok" name="foo" type="text" value="1" />
````