Fix: insert operations in ll shouldnt be able to later the cfg
Fix: insert_element_into_tree() shouldnt be able to alter the cfg
Fix: insert opterations in the avl shouldnt be able to alter the cfg
Fix: Interface for ht_insert(): should not be able to alter cfg
Added implementation for ht_ndel()
Fix: ht_ndel() should not be able to alter the passed cfg
Added implementation for ht_insert()
Merge pull request #195 from matthiasbeyer/fix-insert_const_parameters

Fix: insert operations shouldn't be able to alter `cfg` parameter
Merge pull request #137 from matthiasbeyer/implement-ht_ndel

Added implementation for ht_ndel()
Merge pull request #161 from matthiasbeyer/implement-ht_insert

Added implementation for ht_insert()