Changed to support verbatim target variables in all keys and values, legacy support for Jinja 2.6

* Added traversal (walk) function to parse keys and values for verbatim target variables, i.e. variables of the generated script language
* Added environment functions to temporarily reset the string used for new lines. Needed to work around the missing 'wrapstring' keyword in Jinja 2.6
* Added context function to allow querying context variables by name within templates. Needed to get default values for target variables.