enable Datadog event alerts on Chef failure

Includes changes from #28 - this commit range will auto-update once that one is merged.

When a given Chef run_status is anything other than `success`, the
Event body will add any @ handles that have been provided in an array
through the Handler's configuration.

This feature will go unused until the chef-datadog cookbook has been
updated to use it, which is contingent on determining if there is a
sane upgrade path that does not trigger upgrade of the handler
unintentionally.

Also included is some refactoring of the main `report` to sub-methods, makes code a little more comprehensible.