Split modules out into separate repo

[bmonkman]

As discussed in this proposal: https://docs.google.com/document/d/111E-ud8a6IHSAdZ346hUPOBTtIX2vJ-XkoiJcm4Li6s

To make it easier for people to upgrade and add more clarity on how users should structure their own changes to terraform we should:

• Split all modules except for environment out to a separate repo (a single repo for all, for now)
• Change environment to reference the new modules
• Add documentation and examples to show users where they should add custom terraform
• Review outputs of modules to make sure we are exposing enough from each to make them useful
• Look into setting up auto-deployment of our modules to the terraform registry

[bmonkman]

https://registry.terraform.io/modules/commitdev/zero/aws/0.0.1