MutationObserver for IE. Second try.

This time the MutationObserver polyfill is added after the shadow dom polyfill
and the mutation observer only works with wrapped nodes. It still needs to be
aware of the wrappers since observe can be called with non wrapped nodes.
Merge pull request #142 from arv/more-mutation-observer-ie

MutationObserver for IE. Second try.
Removing syntax highlight for docs
Add unwrapIfNeeded and use it in a few places.
Wrap MutationEvent relatedTarget
Merge pull request #144 from arv/unwrap-if-needed

Add unwrapIfNeeded and use it in a few places.
Merge pull request #145 from arv/wrap-related-node

Wrap MutationEvent relatedTarget
fix submodule path
Update README.md
fix attributions
Merge branch 'master' of github.com:polymer-project/ShadowDOM
update tools
fix submodule paths
Merge pull request #148 from Polymer/master

5/14 master -> stable