streamlineGlobalContext: Support resetting global context before handling request

In streamline, the global context will persist unless you reset it at the beginning of the request. This PR wraps the app.handle method to reset the context before continuing processing the request.

Edit by @aseemk: fixes #12.
Minor typo at the end here. Might also be good to clarify this a bit, maybe link to the source. Suggestion:

```js
// Patch app.handle() to reset Streamline's global context at the beginning of
// every request. This method is only present in Connect's prototype, *not*
// Express's, so we patch proto.init(), which is called on app creation.
// https://github.com/strongloop/express/blob/3.15.2/lib/express.js#L39
```