added web components

I know that Web Components are certainly not production-worthy, but I found myself trying to look up not just Web Components at html5please.com recently, but also Shadow Dom and HTML Templates. I figured that if I'd tried to do that at the site, so did others, so I thought I'd suggest we add a post for them.

I've chosen to collect all the APIs together under the single Web Components heading, since that term is being bandied about a lot and it makes organization easier. The alternative approach would be to add each of the specs (Shadow Dom, Templates, Custom Elements, and Imports) as separate posts, but my current thinking is that putting all of them under the single Web Components post is better (although I should point out that caniuse.com has Shadow DOM independently-listed and may do so for the other specs when they add them).

Divya suggested Dimitri Glazkov's polyfill at JSConf EU 2012 (and I think elsewhere), but Dimitri himself is now recommending people use Polymer Project (which is ambitious), so that's the polyfill I've chosen to focus on (exclusively) in the post.