[push-api] Making pushsubscriptionchange event extendable; defining algorithm (#164)

It was implied that `pushsubscriptionchange` was extendable.  This makes it explicit.

I've also rewritten the event dispatch to conform more closely to the structure in service workers.  I'll create a follow-up that does the same for the `push` event.

Closes #65.
You can view, comment on, or merge this pull request online at:

  https://github.com/w3c/push-api/pull/164

-- Commit Summary --

  * Making pushsubscriptionchange event extendable; defining algorithm

-- File Changes --

    M index.html (67)

-- Patch Links --

https://github.com/w3c/push-api/pull/164.patch
https://github.com/w3c/push-api/pull/164.diff

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/push-api/pull/164