[webcomponents] A couple of new custom elements proposals (#284)

These are largely geared around how we react to [the key custom elements question](https://lists.w3.org/Archives/Public/public-webapps/2015JulSep/0159.html):

- Parser-created constructors assumes we don't want author code to run at those times
- Optional upgrades, optional constructors assumes we do want to allow that
You can view, comment on, or merge this pull request online at:

  https://github.com/w3c/webcomponents/pull/284

-- Commit Summary --

  * Parser-created constructors proposal
  * Optional upgrades, optional constructors proposal

-- File Changes --

    A proposals/Optional-Upgrades-Optional-Constructors.md (253)
    A proposals/Parser-Created-Constructors.md (237)

-- Patch Links --

https://github.com/w3c/webcomponents/pull/284.patch
https://github.com/w3c/webcomponents/pull/284.diff

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/webcomponents/pull/284