Added documentation for valid event types

Reference: http://docs.aws.amazon.com/AutoScaling/latest/APIReference/API_DescribeAutoScalingNotificationTypes.html
Added documentation for valid event types

Reference:
http://docs.aws.amazon.com/AutoScaling/latest/APIReference/API_DescribeAutoScalingNotificationTypes.html
Added documentation for missing parameter 'tags'
Merge pull request #1807 from j0nes2k/develop

Added documentation for valid auto scaling event types and tags. Fixes #1807.