格式化一个字符串是，可以用这样一个组合格式：{index[,alignment][:formatString]}
在 format string 中可能会用到一些转义字符 (escape character)
| \' | a single quote |
| \" | a double quote |
| \\ | a backslash |
| \0 | a null character |
| \a | an alert character |
| \b | a backspace |
| \f | a form feed |
| \n | a new line |
| \r | a carriage return |
| \t | a horizontal tab |
| \v | a vertical tab |
| \uxxxx | a unicode character hex value (e.g. \u0020) |
| \x | same as \u, but you don't need leading zeroes (.g. \x20) |
| \Uxxxxxxxx | a unicode character hex value (longer form needed for generating surrogates) |
