[Specs-cx] Added Examples

[Nat Sakimura]

Hi.

I have included the example proposal and contract and committed to github.

The example still does not include a sensible template. We are going
to replace it soon.
At the moment, we are thinking of using bookstore example such that
Alice buys a book at Bombay Bookstore and uses OpenID4us payment
service to pay for it.

-- 
Nat Sakimura (=nat)
http://www.sakimura.org/en/
http://twitter.com/_nat_en