v0.35.0

Add `create_before_destroy` for parameter group. Make subnet group optional @aknysh (#110)

what

• Add create_before_destroy for parameter group
• Make the names for parameter & option groups unique
• Make subnet group optional
• Bump module versions
• Update example and terratest

why

• You cannot delete a parameter/option group while it is in use, but you can update a database with a new parameter/option group, so in order to change parameter/option groups, you need to create a new one, install it, then delete the old one
• Some update and destroy operations were failing because resources were being deleted in the wrong order
• If var.db_subnet_group_name is provided, use it and don't create a new Subnet Group
• If var.availability_zone is provided (and var.db_subnet_group_name and var.subnet_ids are not), use var.availability_zone to place the instance into the default VPC or EC2 Classic

related

• Closes #93
• Closes #107
• Closes #108
• Closes #109