Detect alternative languages

[pqvst]

A site that supports multiple languages typically includes link alternative tags. It would be nice if linkinator detected and checked these links. This would help to verify that none of the alternative links are broken, and to find these pages if they aren't linked to elsewhere.

For example:

<link rel="canonical" href="[http://localhost:3000/](view-source:http://localhost:3000/)">
<link rel="alternate" hreflang="x-default" href="[http://localhost:3000/](view-source:http://localhost:3000/)">
<link rel="alternate" hreflang="en" href="[http://localhost:3000/](view-source:http://localhost:3000/)">
<link rel="alternate" hreflang="es" href="[http://localhost:3000/es](view-source:http://localhost:3000/es)">