A few tweaks

Just wanted to contribute here, feel free to reject or have me submit in separate pull requests.

1. I prefer to put Nagios service/host alerts in downtime if they're resolved in PagerDuty, so I added a config option to specify the number of seconds the downtime will last for (default's 24 hours).
2. Included the author's name in the Ack/Downtime comment.
3. Removed the check command from the PagerDuty incident.