Declarative source linking

Just an idea, but wondering whether we could set things up so that CETEIcean doesn't need to be explicitly given the xml link to load. Maybe a

``` html
<link type="application/tei+xml" rel="alternative">
```

in the header would be enough, and would also be a hint to web crawlers or other non-human agents as to where the source is. CETEIcean could inspect the page source to find the link.
