Small config update

Renamed ErrorHandler method to SetErrorHandler. Updated README

Treat NULL value for slices as empty slice. Improved couple of unit t…

…ests.

Fixed linter error.

Merge pull request RichardKnop#277 from dhui/sqs_ack

Only delete SQS messages after at task successfully processes the message

Fixed linter errors in redis broker.

Updated dependencies.

Merge pull request RichardKnop#248 from Rio/opentracing

feat(tracing): implement trace context propagation using the Opentracing api

Merge pull request RichardKnop#252 from RichardKnop/feature/json-numb…

…ers-precision

Use json.Number when unmarshaling JSON

Update README.md