- Refactoring and rewritten of option-handling related predicates, placed in its
  own module, option_utils.pl.

- Moved module_files/2 to its own module.
Minor bug fix, only if Module is (-) its generation should be ignored
Minor bug fix
- Increased precision of check_unused analysis, now is able to detect unused
  clauses (and not only predicates)

- Improved performance of such analysis
Minor cleaning and reorganization. Fixed minor warnings.
Added hide_var_dynamic/1 facts
Moved tabulator.pl to xtools package
Simplified location_utils.pl using new usage mode of implementation_module
Added a simple text tracer, to perform automatic tracing of a call