Query_Tree / Configuration: ...
  - Query_Tree:
    - fix ..route() syntax errors using first test, fix one semantical error
    - some refactoring, comments
    - refactor other tests to use sets as recipients to allow route testing
  - Configuration: prepare code for writing to configuration file
  - Mailer: prepare code for future refactoring using filter Query
Query_Tree..route(): 3 tests: pass