Todo List

* Adapt more implementations to take opaque key data and a comparison
  function, as in set_func.h, skip_cas_func.c

* Adapt implementations for use in various kernels

* Implement key-pointer/comparison function versions of more structures, in 
  particular, trees

Desired Additions

* It would be attractive to develop an implementation of the priority queue
  implementation described in 

  H. Sundell and P. Tsigas, “Fast and Lock-Free Concurrent Priority
	Queues for Multi-Thread Systems,” in Proceedings of the 17th Inter-
	national Parallel and Distributed Processing Symposium, 11 pp., IEEE
	press, Apr. 2003.

  (A more up-to-date description is available in the Ph.D. thesis of H°akan
   Sundell, Ch. 5.) 

* It would be interesting to compare the CAS skiplist implementation here with
  that in the H°akan Sundell thesis, Ch. 6, which claims to have better 
  efficiency