### Changed
- Span and SpanContext main implementation uses public fields to share data to allow faster serialization and overall Span overhead #398
- `DDTrace\Encoders\SpanEncoder::encode()` now takes an instance of `DDTrace\Data\Span` instead of `DDTrace\Contracts\Span` #398
- `DDTrace\Processing\TraceAnalyticsProcessor::process()` now takes an instance of `DDTrace\Data\Span` instead of `DDTrace\Contracts\Span` #398
- Improve performance of setTag and setResource #398
- Load required PHP files in one go #387
- Load optional PHP files without filesystem check #387