Added Yahoo Japan YConnect example

I also added links to docs for each provider. Not sure if they're the best references.

There seems to be an occasional problem with the sessions. If you test one provider successfully, and then immediately test another one, you get a "state parameter is missing or not matched" error. If you click "back" on the page and retry it, however, it works. I think I'm correctly using separate state names for each provider, so not sure what's happening there.