Sample doc fixes + link to validator

I e-mailed NIST with some corrections to the sample documents. In the meantime, I've incorporated the fixes here to "get the word out" about best practices in slotting Meaningful Use Stage 2 data into C-CDA.  

Summary:

* Fix problem list dates and ages
* Fix status of problem concern acts (concern/problem status should agree)
* Fix extraneous entryRelation in problems
* Fix smoking status (structured observations should be used, and should match human-readable view )


It might also be worth seeing whether S&I Framework's Transitions of Care workgroup has looked through NIST's sample document for conformance to their "companion guide."