v0.19.0: Feature update

As the releases before, this release has 100% test coverage.

Update

• opt.GetEnv now satisfies opt.Required:

When an environment variable that matches the variable from opt.GetEnv is set, opt.GetEnv will set opt.Called to true and will set opt.CalledAs to the name of the environment variable used.
In other words, when an option is required, opt.Required is set, opt.GetEnv satisfies that requirement.

• opt.GetEnv environment variable now shows in help output.

Example:

REQUIRED PARAMETERS:
    --access-key-id <string>        AWS Access Key ID. (env: AWS_ACCESS_KEY_ID)

    --role-arn <string>             Role ARN. (env: AWS_ROLE_ARN)

    --secret-access-key <string>    AWS Secret Access Key. (env: AWS_SECRET_ACCESS_KEY)

OPTIONS:
    --region <string>               Default Region. (default: "us-west-2", env: AWS_DEFAULT_REGION)