text: Title: Baseline support
  Body: Once https://github.com/python-security/pyt/pull/100 is merged this will be do-able.
  
  So a baseline is for when you want to diff between a previous run, (probably of known issues or false-positives) and a current run, 'as a big part of continuous integration', baseline support is super important.
  
  See https://github.com/openstack/bandit as a tool that implements this.
  
  ```python
      parser.add_argument('-b', '--baseline',
                          help='path of a baseline report to compare against '
                               '(only JSON-formatted files are accepted)',
                          type=str,
                          default=None)
  ```
  
  There is also the newly open sourced [`detect-secrets` repo](https://github.com/Yelp/detect-secrets/blob/b16acf1e8dc1e05366a9bfbd7ce35ed611adb94d/detect_secrets/core/baseline.py#L41) from the Yelp security team that implements this.