Cleaner message events from the host
Refactor child messaging into a Guest class
Let's pretend I meant to use ES6 object definitions
Update to use is=responsive-body

You can't register an element and an extension, but you can use the same
prototype for two elements. So we register a second time for the is=...
extension syntax, while still allowing responsive-child to work.
Support is="responsive-iframe" extension
Documentation update
Added documentation for responsive-iframe
Merge branch 'master' into bower
Bower build 0.0.6