Release 1.6.4

ENHANCEMENTS:

• 667: Add writer endpoint type For database clusters
• 668: Allow DB Instance to be edited
• 670: The master username should be a required field
• 673: Convert db-subnet-group subnets into a list
• 677: Enable Point in time recovery for db clusters

ISSUES FIXED:

• 669: Sorts the availability zones of db-cluster so it doesn't update every time
• 671: Fixes null pointer exceptions with db-cluster
• 672: Paginate the refresh call for DbClusterParameterGroupResource to pull all parameters
• 676: Fix null pointer upon db-cluster deletion