Adding initial message error value on Error object.

export interface SqlError extends Error {

  /**

   * Either a MySQL server error (e.g. 'ER_ACCESS_DENIED_ERROR'),

   * a node.js error (e.g. 'ECONNREFUSED') or an internal error

   * (e.g. 'PROTOCOL_CONNECTION_LOST').

   */

  code: string | null;

  /**

   * The error number for the error code

   */

  errno: number;

  /**

   * The sql state

   */

  sqlState?: string | null;

  /**

   * Boolean, indicating if this error is terminal to the connection object.

   */

  fatal: boolean;

}