Validator Fixes:
* Check that there are no nested block HTML elements in an HTML paragraph
* create a warning for UCUM annotations

Other Changes:
* Fix some issues when converting Allergy Intolerance 3 <-> 4
* Fix issues generating invsalid HTML
* Fix up FHIRPath to pass latest test cases 
* Bundle rendering improvements
* Give code interface for control over validation rules
* add support for rendering choice groups (CDA)