code: private void appendLine(final String... fields) throws IORuntimeException {
  		try {
  			doAppendLine(fields);
  		} catch (IOException e) {
  			throw new IORuntimeException(e);
  		}
  	}
docs: 追加一行，末尾会自动换行，但是追加前不会换行
  
  @param fields 字段列表 ({@code null} 值会被做为空值追加)
  @throws IORuntimeException IO异常