Merge branch 'master' of https://github.com/Polymer/docs into rel0.5.0

Conflicts:
	docs/start/platform.md
Cleanup on platform => webcomponents rename.
Updated URL mapping for webcomponents polyfills.
Also tweaked wording.
Merge branch 'master' of https://github.com/Polymer/docs into rel0.5.0
Merge branch 'master' of https://github.com/Polymer/docs into rel0.5.0

Conflicts:
	app.yaml
	docs/start/platform.md
Use minified webcomponents.js.
Merge pull request #728 from arthurevans/rel0.5.0

More cleanup for webcomponents switch