New supervisord collector

In this pull request: a collector for supervisord (http://supervisord.org/) with relevant unit tests and documentation. I started with only a handful of stats ("state" and "uptime") and support for both the default unix socket-based and HTTP-based XML-RPC servers that supervisor can run.  Those cover our team's basic needs for now and it should be straightforward to extend if needed.

Apologies for the commit spam; I went down the path of splitting out a separate wiki submodule and decided to roll that back for a cleaner pull request.