updating Context class to have notion of parent so contexts can be chained while maintaing scope.  Added mutlisource query implementation
fixing a few stylistic issues and implementing ExpressDef caching on root patient context
 adding expressions for Tuple, QueryDefineRef, AliasRef and Property.  Reworked Query exectuion to return tuple from MultiSource queries by default along with a few bug fixes
Adding With and Without filters to queries.  Tests are a bit odd currently as Date range functions are integrated yet
adding simple sorting impl
Fix CQL execution age example and bug that required parameters to be passed to context.  Also re-enabled tests.
merging master into context branch
Merge pull request #4 from cqframework/context_work

Merging in pull request for hierarchical contexts and support for complex queries.