Use entry to create a sidebar entry.
Use this helper to add custom attributes.
Do NOT use this helper to add css styles, as they may not be applied the way
you want/expect if underlying Button styles change.
Instead, please use the css helper.
Use this link for routing within a single page app.
This will make a normal <a> tag, but change the Events.onClick behavior to avoid reloading the page.
See https://github.com/elm-lang/html/issues/110 for details on this implementation.