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_generateResponseDescriptors

@param {object} responses
@returns {object}
function(responses) {
    assert(_.isObject(responses))
    self = this
    var descriptor = function(response) {
      return {
        name: response.statusCode.toString(),
        statusCode: response.statusCode,
        description: response.description,
        schema: self._removeNoDocumentProperties(response.schema),
        example: response.example,
        headers: response.headers.length === 0 ? null : _.join(_.map(response.headers, function(header) {
          return _.trim(header.toString())
        }), '\n')
      }
    }
    return _.sortBy(_.map(responses, descriptor), function (r) { return r.name })
  }