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

exporter/buffer/buffer.go

@@ -0,0 +1,62 @@
+package buffer
+
+import (
+	"sync"
+	"sync/atomic"
+
+	"github.com/open-telemetry/opentelemetry-go/exporter/observer"
+)
+
+type (
+	Buffer struct {
+		observers []observer.Observer
+		events    chan observer.Event
+		dropped   uint64
+		wait      sync.WaitGroup
+		close     chan struct{}
+	}
+)
+
+func NewBuffer(size int, observers ...observer.Observer) *Buffer {
+	b := &Buffer{
+		observers: observers,
+		events:    make(chan observer.Event, size),
+		close:     make(chan struct{}),
+	}
+	b.wait.Add(1)
+	go b.run()
+	return b
+}
+
+func (b *Buffer) Observe(data observer.Event) {
+	select {
+	case b.events <- data:
+	default:
+		atomic.AddUint64(&b.dropped, 1)
+	}
+}
+
+func (b *Buffer) Close() {
+	close(b.close)
+	b.wait.Wait()
+}
+
+func (b *Buffer) run() {
+	defer func() {
+		_ = recover()
+		b.wait.Done()
+	}()
+
+	for {
+		select {
+		case <-b.close:
+			return
+		case ev := <-b.events:
+			// TODO: This has to ensure ordered arrival,
+			// e.g., put into a heap and delay observations.
+			for _, obs := range b.observers {
+				obs.Observe(ev)
+			}
+		}
+	}
+}