Resque monitoring, Per-plugin frequencies, and additional Redis monitoring

Hey there,

In case this is helpful - I've worked on the following in my fork.  I'm successfully running Bipbip on my EC2 servers.  I'll be adding additional work too.  Thanks for your efforts.

* Added a Resque plugin to track worker + queue stats along with test cases
* Added `used_memory_rss`, `mem_fragmentation_ratio`, `connected_clients`, and `blocked_clients` to Redis, with float-rounding for `mem_fragmentation_ratio`
* Allow per-plugin specification of polling frequency.  Tests included.

Note: I've temporarily removed 1.8.7 testing from Travis due to a rubygems compatibility issue. See: https://github.com/bundler/bundler/issues/2784.