Terragen

Add support for [heredoc config](https://www.terraform.io/language/expressions/strings#heredoc-strings), to allow json documents to be passed for iam config, eg


role_json: >
<<EOT

{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Principal": {
"Service": "lambda.amazonaws.com"
},
"Action": "sts:AssumeRole"
}
]
}

EOT

Bugfix release for missing dependency 😊

Added support for creating HCL maps and reading secrets from environment variables. Taken from docs:

Environment Variables and Secrets
It is good security practice to not store secrets in your config. Terragen supports reading values from environment variables. You can set a secret as an environment variable using the `env.` notation, eg:

yaml
my_secret: "env.MY_SECRET"


HCL Maps
Terragen will translate sub-objects in the main `config` object into a [HCL Map](https://www.terraform.io/language/values/variables#map). For example:

yaml
config:
tags:
name: "testMap"
environment: "Test"


Will generate a map as follows:
hcl
tags = {
name = "testMap"
environment = "Test"
}

* Massively improve documentation at ReadTheDocs site
* Simplify configuration of Terragen, hopefully making it more obvious how to get started

Inital release:

- Config pattern working nicely
- Terraform module generation working and tested (on simple cases) but it should work
- AWS Only provider