* update module name

* update license header

* noop test
 * gRPC reporter test
 * tracer parameter test
 * and so on

* Creating noop span when tracer is not inited
 * If the current context contans noop span, other spans are all noop spans

* Add downstream propagation extraction

* Add upstream propagation

* Add span context that links all spans in a local trace context

* Implement Span

- Add gRPC lib
- Add skywalking proto and generate *.pb.go files
- Implement service and instance register

* build system

* segment implement

* circle ci