Update book/src/SUMMARY.md
- [Bitfields](./bitfields.md)
- [Interned strings](./istr.md)
- [#[derive(Format)]](./format.md)
- <!-- - [write!](./write.md) -->
- [Filtering](./filtering.md)
- [#[timestamp]](./timestamp.md)
- [#[global_logger]](./global-logger.md)
