code: func (F *Frisby) SetHeaders(headers map[string]string) *Frisby {
  	if F.Req.Headers == nil {
  		F.Req.Headers = make(map[string]string)
  	}
  	for key, value := range headers {
  		F.Req.Headers[key] = value
  	}
  	return F
  }
docs: // Set several Headers for the coming request