Add benchmarks

[codefromthecrypt]

We have to be careful that the overhead here doesn't go nuts by accident. We should have scenarios including parsing multiple states with provisioning, especially the TTL logic.

See https://github.com/openzipkin/brave/tree/master/instrumentation/benchmarks/src/main/java/brave/propagation - for benchmarking the general flow

See https://github.com/openzipkin/zipkin/blob/master/benchmarks/src/main/java/zipkin2/internal/ReadBufferBenchmarks.java - for benchmarking the TODO more efficient TTL read/write #28