audit license headers
Make `set` chainable

`.set` should return self, according to the spec https://people.mozilla.org/~jorendorff/es6-draft.html#sec-weakmap.prototype.set
Test chaining of .set
Merge pull request #11 from dfcreative/patch-1

Make `set` chainable
Update README.md

Deprecated in favor of https://github.com/Polymer/webcomponentsjs
Merge remote-tracking branch 'upstream/master'