Added packet assertions to wick test cases

[jsoverson]

This PR adds the concept of assertions and operators to wick tests to improve the flexibility of test cases.

There are 5 initial operators, LessThan, GreaterThan, Equals, Regex, and Contains with Contains being the only one implemented right now. The former four are self-explanatory. Contains is a loose deep equality.

tests:
  - with:
      url: '{{ctx.env.HTTPBIN}}'
    cases:
      - operation: post
        inputs:
          - name: id
            value: '1'
          - name: name
            value: 'wick'
        outputs:
          - name: body
            assertions:
              - operator: Contains
                value:
                  form:
                    from_root: 'nas.glhf.lan:9888'
                    id: '1'
                    name: 'wick'
          - name: response
            assertions:
              - operator: Contains
                value:
                  status: '200'
              - operator: Contains
                value:
                  version: '1.1'