enable the ability to do value comparisons in addition to equivalency checks

I added this PR to fill a need where I needed to set up some alerting based on query results from elastic search.

This PR adds several features...
- The ability to post data to the url
- The ability to retrieve a nested key from a json response for value comparision as part of the check
- The ability to use greater-than/less-than comparisons in addition to equivalency (which was already supported)