[maven-release-plugin] copy for tag 5.2.0

Optimizes internal trace context related code, especially extra

After some trial and error with benchmarking, I found
`MutableTraceContext` is not enough a win unless we change api, which we
can't until Brave 6. Meanwhile, this optimizes as much as possible,
notably eliminating as many arraylist creations (from extra) as
possible.

[maven-release-plugin] copy for tag 5.1.5

Fixes OSGi setup, missing for brave-instrumentation-http (openzipkin#743

)

[maven-release-plugin] copy for tag 5.1.4

Clarifies the intent of sampled status

[maven-release-plugin] copy for tag 5.1.3

Bumps to latest zipkin

[maven-release-plugin] copy for tag 5.1.2

version bump