Implement http close notifier (awslabs#47)

* implement http.CloseNotify

* Removing defer

Fix ProxyWithContext to use original context (awslabs#42)

Add echo support (awslabs#36)

* support for [echo framework](https://github.com/labstack/echo)

Release 0.3.0 with Lambda context support

Release 0.2.0