working on slf4j debug messages

- fixed docu spelling typo
- updated preprocessor-testing to not require handler-jadds as input anymore
- grammar: removed obsolete DefinitionFileName from Handler
- Compiler: revert to standard-out/-err instead of JUL for logging (slf4j did not work here)
- Compiler: remove temporary code to create empty handler files
- Compiler: add some documentation snippets
- use slf4j loggers in tests instead of log4j ones
- always use slf4j as logTarget in tests
- update log4j impl to 2.17.1 in tests