Fix invalid HTML5

[Rotzbua]

Since this useful framework relies on native HTML, it would be good to use formally correct HTML in the documentation and examples.

The following facts are relatively unknown or ignored:

In HTML, a void element must not have an end tag. For example, `<input type="text"></input>` is invalid HTML.
Self-closing tags (<tag />) do not exist in HTML.

Source: https://developer.mozilla.org/en-US/docs/Glossary/Void_element