delete files without any use
del joo15 specific file
improve self documentation
Joomla 3 API compliant

modif based on doc Potential backward compatibility issues in Joomla 3
and Joomla Platform 12.2 at

http://docs.joomla.org/Potential_backward_compatibility_issues_in_Joomla_3_and_Joomla_Platform_12.2