* feature/3.0:
Alter ContextCarrier, add applicationCode and peerHost
remove a test main.
Fix compile issue.
Add a new field, applicationCode, in TraceSegment.
Add a log field.
Fix ‘tags.get’ cause ClassCastException, because after akka-message/serialize, all tags values are type of String.class.
Fix serialize bugs.
Add ISerializable interface, and implement this interface in ‘TraceSegment’, ‘TraceSegmentRef’, ‘Span’, ‘LogData’
Add the trace proto file.
Fix some compile issues. Add protobuf dependency, and protoc-grpc-plugin.
Fix log-toolkits(log4j, log4j2, logback) compile issue.
Fix opentracing-toolkit activation compile issue, and useless codes.
# Conflicts:
# pom.xml
Give a new demo AbstractWorkerProviderTestCase.
wusheng
pengys5
ascrutae