refactor(index.js): Add base classes of Transport and Metric to export

index.js

@@ -1,11 +1,15 @@
 import UMetrics      from './UMetrics';
+import Transport     from './transport/Transport';
 import PullTransport from './transport/PullTransport';
 import PushTransport from './transport/PushTransport';
+import Metric        from './metric/Metric';
 import GaugeMetric   from './metric/GaugeMetric';
 
 export {
 	UMetrics,
+	Transport,
 	PushTransport,
 	PullTransport,
 	GaugeMetric,
+	Metric,
 };