Added notifier for the Pushover notification service.
Changed default Pushover notifier priority.
Changed the limit of message size to 512 characters from 512-(title length) in Pushover notifier.
Refactored use of super class initializer in PushoverHandler.
Added relevant documentation for PushoverHandler.
Changed PushoverHandler to set priority to 0 (instead of -1) if an invalid priority is given.
Added extra documentation for PushoverHandler.
Merge pull request #114 from owo/master

Pushover notifier