Creates a internal facing logging interface

This is a simple loggin interface to be used interally for the sdk.
Included is an exmaple in `namedtracer` run:
```
cd example/namedtracer
go run . >/dev/null
```

sdk/trace/batch_span_processor.go

@@ -22,6 +22,7 @@ import (
 	"time"
 
 	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/internal/debug"
 	"go.opentelemetry.io/otel/trace"
 )
 
@@ -224,6 +225,7 @@ func WithBlocking() BatchSpanProcessorOption {
 
 // exportSpans is a subroutine of processing and draining the queue.
 func (bsp *batchSpanProcessor) exportSpans(ctx context.Context) error {
+
 	bsp.timer.Reset(bsp.o.BatchTimeout)
 
 	bsp.batchMutex.Lock()
@@ -236,6 +238,7 @@ func (bsp *batchSpanProcessor) exportSpans(ctx context.Context) error {
 	}
 
 	if l := len(bsp.batch); l > 0 {
+		debug.Log.V(5).Info("exporting spans", "count", len(bsp.batch))
 		err := bsp.e.ExportSpans(ctx, bsp.batch)
 
 		// A new batch is always created after exporting, even if the batch failed to be exported.