Ccda generation

As I mentioned on #82, I just discovered that it's going to be basically impossible to generate CCDAs from a variety of charts that still pass MU Stage 2 without using Model Driven Health Tools to generate the CCDAs, so I'm having to switch gears from this template-based approach.

== Current Status ==
There are several sections required for a valid Clinical Summary CCDA still missing here:
1. Social history / smoking status
2. Instructions
3. Assessment/Plan

There are also strict standards around valid codes enforced by the Testing Transport Tool that are very difficult to comply with (it rejects lots of the codes in the HL7 sample we use to test CCDAs).

However, I suspect that this is still approaching a useful state for practical data interchange even if doesn't pass TTT's standards, so I still wanted to share. @blacktm, what's your opinion on whether we should keep this on a separate branch on the core fork or try to merge it to master? The latter means we have to keep the template up-to-date as the JSON changes; the former lets us avoid that but obviously means the branch is more likely to decay. So I think it comes down to whether we think this is useful enough in its present state (or a slightly modified future state) to want to maintain.