Harden tsclient's zeromq publisher/subscriber against slow consumers

[cuveland]

These changes limit publisher and subscriber buffer sizes to favor dropping items instead of queueing. This should help online monitoring software to work on recent data and prevent extensive memory consumption.

In addition, these changes create an enviroment in which the zeromq publish/subscribe can be tested:

• Add InputArchiveLoop class and input-archive-cycles parameter to tsclient.
• Add rate-limit parameter to tsclient.