Sceptre

- Adding support for Troposphere 1.8.
- Adding stack protection support.
- Adding support for allowing Troposphere templates to import modules from
parent directories.
- Adding documentation section for IAM role setup.
- Fixing bug in update-wth-cs command.

- Adding require_version.
- Renaming --machine-readable to --output.
- Refactoring hook.py.

- Improving logging.

- Updating CONTRIBUTING.rst.

- Fixing multithreaded S3 bucket create bug.

- Deprecating the CLI flags --iam-role, --profile, --region.