Add negation syntax for headers

[decoomanj]

Sometimes you want to explicitly test if certain headers are missing.

A possible syntax could be;

headers:
  - !Content-Type

[j-musca]

@decoomanj The exclamation mark is a reserved keyword in yaml. It would be much easier to introduce a new field "forbiddenHeaders", "illegalHeaders", etc.

[j-musca]

Current format

  response:
    headers:
      Content-Type: 'application/json; charset=utf-8'
    status: 201

Option "new field"

  response:
    headers:
      Content-Type: 'application/json; charset=utf-8'
    forbiddenHeaders:
      - X-Custom-Header-0
      - X-Custom-Header-1
    status: 201

Option "using headers field"

  response:
    headers:
      Content-Type: 'application/json; charset=utf-8'
      "!X-Custom-Header-0":
      "!X-Custom-Header-1":
    status: 201

[decoomanj]

It would be cool to improve the testing of headers with regex. It gives the power to test normal, static strings, but does also the negation, patterns, etc. The only problem is the syntax in YML.