Add support for multiple PagerDuty Services

-- More // hints in config file on how to properly setup single/multiple service ids
-- If Single service_id, convert it to an array. If Multiple service_id, don't do anything
-- Sanitize the service_id. It should be 7 characters A-Z0-9
-- Add additional logging
-- Refactor the check if there are zero incidents (previously it breaks from the function).
Merge pull request #32 from dobber/master

Add support for multiple PagerDuty Services