Add r_set_cfg parameter to ll_destroy
Add r_set_cfg parameter to ll_insert_data
Remove old helper functions
Rename ll_insert_data to ll_insert
Add r_set_cfg parameter to ll_delete
Remove old unused function
Make user defined free'ing function optional
Remove tests for nonexisting functions
Adapt tests to new ll interface
Modify definition of ll_insert
Modify definition of ll_delete