code: func ErrorHandler(errs Errors, resp http.ResponseWriter) {
  	if len(errs) > 0 {
  		resp.Header().Set("Content-Type", jsonContentType)
  		if errs.Has(DeserializationError) {
  			resp.WriteHeader(http.StatusBadRequest)
  		} else if errs.Has(ContentTypeError) {
  			resp.WriteHeader(http.StatusUnsupportedMediaType)
  		} else {
  			resp.WriteHeader(StatusUnprocessableEntity)
  		}
  		errOutput, _ := json.Marshal(errs)
  		resp.Write(errOutput)
  		return
  	}
  }
docs: // ErrorHandler simply counts the number of errors in the
  // context and, if more than 0, writes a response with an
  // error code and a JSON payload describing the errors.
  // The response will have a JSON content-type.
  // Middleware remaining on the stack will not even see the request
  // if, by this point, there are any errors.
  // This is a "default" handler, of sorts, and you are
  // welcome to use your own instead. The Bind middleware
  // invokes this automatically for convenience.