Flesh out widget lifecycle and enhance widgets.register

* Widget lifecyle methods of create, inserted and removed
* Returns from lifecycle methods promise aware
* Allow generational inheritance for base in registration
* Flesh out unit tests for _Widget and widgets
Add the ability to hide and show widgets.

* Add `.hide()`, `.show()` and `.isHidden` to _Widget
* Create class `pd-hidden`
Add documentation, modify _Widget lifecycle.

* Align _Widget lifecycle to evolving standards
* Add documentation around _Widget
* Update README to point at documentation
Auto-attach event support

* _Widget now supports auto-attachment of events based on the
  `.events` property.
Adding todomvc, partially working.
Fix link in README
Complete examples/todomvc

* Add support for binding delegates for pidgin/tmpl
* Modify the widget lifecycle to better support event attachment
* Warn when selector events cannot identify a specific node
* Add _Widget.query() syntactic sugar
Update lib/core
Update lib/core
Move from Polymer/platform to Polymer/CustomElements

* Remove dcl
* Remove Polymer/platform
* Add Polymer/CustomElements
Update tests/client.html to utilise only CustomElements
Update lib/core