Support for executing Oracle PL/SQL with boolean parameters

This PR is targeting issue #80

- [x] Procedures with BOOLEAN input arguments
- [x] Functions with BOOLEAN input arguments
- [x] Procedures with BOOLEAN output arguments and without BOOLEAN input ones
- [x] Procedures with both BOOLEAN output and BOOLEAN input arguments
- [x] Procedures with BOOLEAN **in out** arguments
- [x] Functions without BOOLEAN **out** or **in out** arguments
- [x] Functions with BOOLEAN **out** or **in out** arguments
- [x] Make sure all combinations of these are covered
- [ ] Add some example to the documentation

Boolean literals **true** and **false** are expected in lower case in DbFit tests.