Adding tags, KMS Support, Customizing some periods

[AndrewFarley]

Added the following features:

• Adding KMS-related alarms from the recommended Elasticsearch Cloudwatch Alarms page
• Making this module support tagging of resources created
• Making some (normally) noisy alarms allow customizing their period to make them a bit quieter
• Cleaned up the README, added references to AWS's recommended alarms, updated to add new features
• Removed unnecessary monitor_insufficient_available_nodes, in favor of enabling this automatically if the number of nodes are specified, altered the default to be 0.
• Fixed a bug in the min available nodes to be < and not <=

Please do a release after this merge so everyone can leverage it. ;) Thanks!

[AndrewFarley]

@dubiety When you get a chance. Cheers!