priority: An integer between -1 and 2, indicating low (-1),
normal (0), high (1), or emergency (2) priority.
+ retry: An integer specifying how often, in seconds, to resend
+ the notification until acknowledged. Must be 30 or
+ greater. Requires a priority value of 2.
+ expire: An integer specifying when, in seconds, to stop
+ resending the notification. Must be 86400 or less.
+ Requires a priority value of 2.
url: A string of up to 500 characters containing a URL
to attach to the notification.
url_title: A string of up to 50 characters containing a