There was emmense work to prepare for decoupling of spring-cloud-sleuth-core
from Zipkin. This included complete test conversion and deprecations between
2.2.x and 3.0.x.
This moves all Zipkin related code to spring-cloud-sleuth-zipkin, making the
primary data recording tool `SpanHandler` as opposed to `Reporter<zipkin2.Span>`
For example, Wavefront and soon Stackdriver can implement `SpanHandler` and
skip conversion into the Zipkin model first. `SpanHandler` also includes
begin and end hooks which allow data extensions to be developed.
see https://github.com/wavefrontHQ/wavefront-spring-boot
4ed3db9a27