move implementation to internal/ directory (#828)

internal/logger/stderrlogger.go

@@ -0,0 +1,23 @@
+package logger
+
+import (
+	"fmt"
+	"os"
+)
+
+type stderrLoggerOutlet struct{}
+
+func (stderrLoggerOutlet) WriteEntry(entry Entry) error {
+	fmt.Fprintf(os.Stderr, "%#v\n", entry)
+	return nil
+}
+
+var _ Logger = testLogger{}
+
+func NewStderrDebugLogger() Logger {
+	outlets := NewOutlets()
+	outlets.Add(&stderrLoggerOutlet{}, Debug)
+	return &testLogger{
+		Logger: NewLogger(outlets, 0),
+	}
+}