Added support for content-available in Grocer::Notification
Got rid of magic number and made it clearer that the value passed to content_available= isn't used.
Distinguish between truthy and falsy in content_available.
Should test for absence of key in hash, not for its value being nil.
Cleaned up falsy content_available test.
Updated docs for content_available.
Updated docs for content_available to match the other keys in the payload.
Merge pull request #58 from somezack/add_content_available

Added support for content-available