Add function for freeing an item to the set cfg
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
Merge pull request #113 from neithernut/mod-ll-interface

Mod linked list interface
Added avl_ndel() interface
Merge pull request #112 from matthiasbeyer/add-interface_avl_ndel

Added avl_ndel() interface