first version of the encounters
Update documents for encounters
Added identifiers and  changed from code to value
allergies and encounters are added to ccd
- code_system->code_system_name
- remove all uris
Correct allergies codeSystem to code_system_name
Updated the document for code_syetm->code_system_name
Merge branch 'master' into matt-immunizations

Conflicts:
	docs/model.md