* Override extension methods in BackboneElement to look in modifierExtensions as well as extensions
* First draft of Profile Comparison tools (org.hl7.fhir.r5.comparison)
* Improved error messages when snapshot generation fails when slicing something that doesn't repeat
* Improvements for CDA round-tripping (XML esacping issues, xsi:type related issues, namespacing issues)
* Fix bug rendering DiagnosticReports with multiple categories
* adjust check on Attachment to only be an warning (when no meaningful content exists)
* add security check mode to Validator