ShadowDOM <3 MutationObserver

If MutationObserver polyfill is added after the shadow dom polyfill this should
work. Since observe is sometimes called with non wrapped nodes we need to wrap
in that case.
rebase
Merge pull request #4 from arv/after-shadow-dom

ShadowDOM <3 MutationObserver
fix attribution
update urls
Merge pull request #5 from Polymer/master

5/14 master -> stable