tracing-core 0.1.20

This release adds support for f64 as one of the tracing-core
primitive field values, allowing floating-point values to be recorded as
typed values rather than with fmt::Debug. Additionally, it adds
NoSubscriber, a Subscriber implementation that does nothing.

Added

• subscriber: NoSubscriber, a no-op Subscriber implementation
  (#1549)
• field: Added Visit::record_f64 and support for recording
  floating-point values (#1507)

Thanks to new contributors @jsgf and @maxburke for contributing to this
release!