Golang opentelemetry-go draft API (incomplete) (#9)

* Work in progress from https://github.com/lightstep/opentelemetry-golang-prototype

* Renames

* Rename

* Finish rename

* Rename packages

* README

example/http/client/client.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/open-telemetry/opentelemetry-go/api/tag"
+	"github.com/open-telemetry/opentelemetry-go/api/trace"
+	"github.com/open-telemetry/opentelemetry-go/plugin/httptrace"
+
+	_ "github.com/open-telemetry/opentelemetry-go/exporter/loader"
+)
+
+var (
+	tracer = trace.GlobalTracer().
+		WithService("client").
+		WithComponent("main").
+		WithResources(
+			tag.New("whatevs").String("yesss"),
+		)
+)
+
+func main() {
+	client := http.DefaultClient
+
+	ctx := tag.NewContext(context.Background(),
+		tag.Insert(tag.New("username").String("donuts")),
+	)
+
+	var body []byte
+
+	err := tracer.WithSpan(ctx, "say hello",
+		func(ctx context.Context) error {
+			req, _ := http.NewRequest("GET", "http://localhost:7777/hello", nil)
+
+			ctx, req, inj := httptrace.W3C(ctx, req)
+
+			trace.Inject(ctx, inj)
+
+			res, err := client.Do(req)
+			if err != nil {
+				panic(err)
+			}
+			body, err = ioutil.ReadAll(res.Body)
+			res.Body.Close()
+
+			return err
+		})
+
+	if err != nil {
+		panic(err)
+	}
+
+	fmt.Printf("%s", body)
+}