Add GlobalTracer and ActiveSpan

[arugal]

GlobalTracer

tracer, _ := NewTracer("service")

// registers `tracer` as the global Tracer.
SetGlobalTracer(tracer)

// returns the registered global Tracer
tracer1 := GetGlobalTracer()

ActiveSpan

tracer, _ := NewTracer("service")
_, ctx, err := tracer.CreateLocalSpan(context.Background())
if err != nil {
  t.Error(err)
}

activeSpan := ActiveSpan(ctx)

resolve #96

[github-actions]

license-eye has totally checked 294 files.

Valid	Invalid	Ignored	Fixed
2	52	240	0

Click to see the invalid file list

• .github/workflows/ci.yaml
• .github/workflows/plugin_test.yaml
• .licenserc.yaml
• Makefile
• config_discovery.go
• config_discovery_test.go
• correlation.go
• correlation_test.go
• doc.go
• example_trace_test.go
• golangci.yml
• internal/idgen/idgen.go
• internal/idgen/idgen_test.go
• internal/tool/error.go
• internal/tool/os_util.go
• internal/tool/time.go
• log/context.go
• log/context_test.go
• log/doc.go
• noop.go
• noop_test.go
• plugins/http/client.go
• plugins/http/doc.go
• plugins/http/example_http_test.go
• plugins/http/server.go
• plugins/http/test/client/client.go
• plugins/http/test/docker/Dockerfile.http_client
• plugins/http/test/docker/Dockerfile.http_server
• plugins/http/test/docker-compose.yml
• plugins/http/test/expected.data.yml
• plugins/http/test/http_plugin_test.yaml
• plugins/http/test/server/server.go
• propagation/propagation.go
• propagation/propagation_test.go
• reporter/doc.go
• reporter/grpc.go
• reporter/grpc_test.go
• reporter/log.go
• sampler.go
• sampler_test.go
• segment.go
• segment_test.go
• span.go
• span_opts.go
• span_test.go
• test/e2e/example-server/main.go
• trace.go
• trace_context.go
• trace_context_test.go
• trace_opts.go
• trace_propagation_test.go
• trace_test.go

[codecov-commenter]

Codecov Report

Merging #145 (b23a5f4) into master (0f9874e) will increase coverage by 0.47%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #145      +/-   ##
==========================================
+ Coverage   70.38%   70.86%   +0.47%     
==========================================
  Files          17       18       +1     
  Lines         915      930      +15     
==========================================
+ Hits          644      659      +15     
  Misses        224      224              
  Partials       47       47              

Impacted Files	Coverage Δ
trace.go	82.47% <ø> (ø)
trace_context.go	100.00% <100.00%> (ø)
trace_state.go	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0f9874e...b23a5f4. Read the comment docs.