Co-authored-by: 吴晟 Wu Sheng <wu.sheng@foxmail.com>

* fix ParentEndpointID bug

* language

* update module name

* update license header

* Adding more unit test cases including

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

* Add http plugin

* Add essentail tags

* Add component

* Add log reporter for examples

* Polish codes

* 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

* build system

* segment implement

* circle ci