[webcomponents]: Making <link rel="components"> produce DocumentFragments

Hi folks!

Just had a quick discussion with Elliott and he suggested that instead of
building full-blown Documents, the <link rel="components"> just make
DocumentFragments, just like <template> does.

Looking at
http://www.whatwg.org/specs/web-apps/current-work/multipage/dom.html#the-document-object
and
the bunch of APIs that will never be useful on a document without a
browsing context, I think it's a pretty good idea. It should make also
components more lightweight.

The only problem is that now I have to figure out how to specify this
without just flat-out stealing, err... I mean reusing, large swaths of
HTML5 spec. But I'll take this one for the team.

:DG<