tracing-core 0.1.28

This release of tracing-core adds new Value implementations, including one
for String, to allow recording &String as a value without having to call
as_str() or similar, and for 128-bit integers (i128 and u128). In
addition, it adds new methods and trait implementations for Subscribers.

Added

• Value implementation for String (#2164)
• Value implementation for u128 and i28 (#2166)
• downcast_ref and is methods for dyn Subscriber + Sync,
  dyn Subscriber + Send, and dyn Subscriber + Send + Sync (#2160)
• Subscriber::event_enabled method to enable filtering based on Event field
  values (#2008)
• Subscriber implementation for Box<S: Subscriber + ?Sized> and
  Arc<S: Subscriber + ?Sized> (#2161)

Thanks to @jswrenn and @CAD97 for contributing to this release!