v2.2.0

Added

• The Spandex.Trace struct now includes priority and baggage fields, to
  support priority sampling of distributed traces and trace-level baggage,
  respectively. More details about these concepts can be found in the
  OpenTracing documentation. An updated version of the spandex_datadog
  library will enable support for this feature in terms of the
  Spandex.Adapter and Sender APIs.

Changed

• It is no longer required that you specify the env option. If not specified,
  it will default to nil. This is useful, for example, for allowing the
  Datadog trace collector configured default to be used.
• The Spandex.Adapter.distributed_context/2 callback now expects a
  SpanContext struct to be returned, rather than a Map.
• Similarly, the Spandex.continue_trace function now expects a SpanContext
  struct rather than a separate trace_id and span_id.
• The sender API now calls the send_trace function, passing in a
  Spandex.Trace struct, rather than passing a list of Spandex.Span structs.
  This means that you need to update the spandex_datadog to a compatible
  version.

Deprecated

• Spandex.continue_trace/4 is deprecated in favor of
  Spandex.continue_trace/3
• Similarly, Tracer.continue_trace/4 is deprecated in favor of
  Tracer.continue_trace/3