Merge to bring both repos in line

This is a response to Jay's issue,
https://github.com/rackspace-cookbooks/cookbook-cloudmonitoring/issues/8

I pulled your current master branch and merged it with ours. There are two updates I kept in from our branch that I'd like to see upstream.

1. libraries/cloud_monitoring.rb
I updated get_entity_by_ip to not fail if you had entities that had no IPs associated

2. README.md
Ryan added extra documentation for Agent Plugins

I also bumped the minor version number and ran a few tests against Ubuntu Public Cloud servers. Let me know if this works for you guys.

In the future we'll keep our changes in branches, so that our master is always the same or behind yours.

Thanks,
Thomas C
Rackspace