1.7

Highlights:
+ Add Slack alerter
+ Add Command monitor
+ Add pkg audit monitor
+ Add Amazon SES alerter
+ Add support for alerters to repeat
+ Support username/password and SSL support for SMTP
* Use subprocess everywhere
* Honour gap configuration option
* Use HTTPS for BulkSMS API
* Use UTC everywhere for times; should fix monitors which have been down -1 hours
* Teach the host (ping) monitor to use command line options better on
different operating systems
* Verify dependencies exist
* Stop alerters from firing success notifications out-of-hours