adding toCql method
merging from github
adding trackback info to Expression to identify the expressions within the source document.  Added stubbed out evaluate method to expression for creating a simple poc runtime.  Added Context and callable interfaces for enabling poc runtime evaluation
adding Trackable assertions to existing expression tests to ensure that they each receive a trackback object and a uuid
merging from github repo.  Reformated code to make it more consistent and organized the imports to eliminate unused imports
fixing bug that was introduced during merge where dataCriteria was not set on the RetrieveExpression