Track Custom Element rewrite changes

[tbranyen]

Reference: WICG/webcomponents#405

Since the Custom Element API is still in flux, I've only implemented the API that matches current browsers. I'll be starting on an opt-in to try out the new API. I'm thinking something like diff.enableExperimental() which matches enableProllyfill() except brings in the new APIs and will change with the leading browser implementation.

[tbranyen]

So much has changed since then... it's gotten a rewrite since the last rewrite. It's out of control so I'm going to rip out of this library until it stabilizes.

[jamesplease]

slight preference for:

enableProllyfill({experimental: true}); if this ever comes to be

[tbranyen]

Closing this out, since I'm going to leave it to the browser vendors to settle on a standard and then we'll revisit.