Add support for button_to

[aidandamerell]

Current sweet alert is not triggered when a button_to tag is used. This should act in the same way a link_to or submit_tag works but the module doesn't define a function for button_to, only button_tag. E.G. <%= button_to "Click Me", root_path, data: { confirm: "Do it?" }, class: "ui button" %>

[smmr0]

see #9