Terraguard

* Updating the CLI to support `--master-config` argument. The master config will always be loaded first and its dictionaries will all be updated by project level configs for now. Plans to see if we can do better here in future.
* Refactored `--plan-file` to `--json-plan-file` for clarity.
* Support for lists of variables that must exist at a resource level.

Major refactor to back track on the initial plan of having resources represented as classes. Opted instead to gain some code maintainability / easier to obtain wider feature set at the cost of allowing users to easily define bas configs (note that doing so is harmless, you just won't get very far).

We can now also define rules at both a resource and a resource attribute level.
e.g. assert that a resource has tags, but also that those tags equal a given value.

Initial Release

Basic support for the AWS terraform providers that fall into the following name spaced resource addresses:
* `aws_ec2`
* `aws_ecr`
* `aws_elb`
* `aws_lb`
* `aws_sqs`
* `aws_vpc`

Functionality

Enforce that attributes must_contain, must_not_contain and must_equal. Tested and working nicely for following use cases:
* `cidr_blocks` must not contain `0.0.0.0/0`
* `tags` must contain certain values, values must be given types.