add C generic and void pointer-less linked list implementation
add ll_front ll_back LL_FOR_EACH
add {pop,remove}_any - remove/pop any node, including the tail and remove_by_value
fix bug in ll_pop_next_any, that checks for removing tail.
use printing macro in the singly linked int ll test
add support for doubly linked lists, and tests for it, to C_stl
add some move semantics and rvalue tests
add dll_pop to doubly linked list