Reimplementation of the zring class with equipotent API

Problem: The zring_node_t type and zring_goto method expose internals of the container and are dangerous, zrings zhash part is also unneccessary when a simple doubly linkes list is needed

Solution: Rename zring to zhashring where it can die in peace, implement a simpler zring class with equipotent elements, remove dangerous elements from zhashring