v0.15.0

Added

• More resource detectors #573

Changed

• Expose the Error type to allow users to set custom error handlers #551
• Allow users to use different channels based on runtime in batch span processor #560
• Move Unit into metrics module #564
• Update trace flags to match spec #565

Fixed

• Fix debug loop, add notes for #[tokio::test] #552
• TraceState cannot insert new key-value pairs #567