humane version history

v0.5.0

Switch from exp/slog to log/slog and from exp/slices to slices now that Go 1.21 has been released.
Adjust the NewHandler function to match the latest slog API.
Use a pointer to sync.Mutex rather than sync.Mutex. See this discussion in the guide to writing slog handlers for why: https://bit.ly/3s2KrOG.
Add testing/slogtest.
Fix a bug (found thanks to testing/slogtest): move the test for Attr.Empty to catch all empty attrs.
Fix a bug (found thanks to testing/slogtest): make sure to call Resolve on all attribute values.