v4.0.0

This is a major refactor adding support for Terraform 0.13 features

• incompatible change minimum required terraform version is now 0.13.0
• incompatible change folders module renamed to folder
• incompatible change iam-service-accounts module renamed to iam-service-account
• incompatible change all iam_roles and iam_member variables merged into a single iam variable. This change affects most modules
• incompatible change modules like folder, gcs, iam-service-account now create a single resource. Use for_each at the module level if you need multiple instances
• added basic variable validations to some modules