Support Alpine.js-like attributes

[marcoroth]

This pull request adds support for properly converting non-standard Alpine.js attributes, like:

<button @click.prevent="something">Button</button>

Now converts to:

button("@click.prevent": "something") { "Button" }

instead of:

button(click.: true, prevent: %(something)) { %(Button)
 }

Resolves #284

Blocked by sparklemotion/nokogiri#3125