Merge pull request go-kit#550 from yurishkuro/ys-fix-549

Simplify and fix unstable test

log/level: remove outdated comment

Release 0.3.0

Merge pull request go-kit#330 from basvanbeek/master

follow opentracing-go refactoring of HTTPHeadersCarrier

Merge pull request go-kit#287 from go-kit/addsvc-errors

examples/addsvc: more sophisticated error encoding