Problem: list and hash container APIs are messed up

There are a lot of good ideas in the new API yet the results are a
mishmash of old and new, without a clear route to a nice clean API.
The zring class was an attempt to fix this, yet it made things more
complex, not simpler.

I'm going to do this in stages:

* Deprecate the v2 classes, using the same names. This does not
  break existing applications. I'll remove some of the new messy
  code from these classes in a second step.

* Create new classes called zlistx and zhashx which initially look
  just like the old ones. I'll clean these up separately.