tracing 0.1.29

This release adds support for recording Option<T> where T: Value as
typed tracing field values. It also includes significant performance
improvements for functions annotated with the #[instrument] attribute
when the generated span is disabled.

Changed

• tracing-core: updated to v0.1.21
• tracing-attributes: updated to v0.1.19

Added

• field: Value impl for Option<T> where T: Value (#1585)
• attributes: - improved performance when skipping
  #[instrument]-generated spans below the max level (#1600, #1605,
  #1614, #1616, #1617)

Fixed

• instrument: added missing Future implementation for
  WithSubscriber, making the WithDispatch extension trait actually
  useable (#1602)
• Documentation fixes and improvements (#1595, #1601, #1597)

Thanks to @BrianBurgers, @mattiast, @DCjanus, @oli-obk, and @matklad for
contributing to this release!