Added debug print helper for linkedlist
Added debug printing for ll_destroy()
Added debug printing for ll_insert()
Added debug printing for ll_delete()
Merge pull request #152 from matthiasbeyer/add-debug_printing_ll

Add debug printing for ll
Added set.c file and r_set type implementation
Reimplement adl_add
Merge pull request #163 from neithernut/reimplement-avl_add

Reimplement avl_add
Merge pull request #178 from matthiasbeyer/implement-r_set_type

r_set type implementation
Added set.c to CMakeLists.txt
Merge pull request #185 from matthiasbeyer/add-set_c_cmakelists_entry

Added (missing) entry for set.c in CMakeLists.txt
Added implementation for ht_insert()
Fixup: Renaming function: avl_add() -> avl_insert()
Fixup: avl_insert() returns status now