Reduce confusion for "magic" binding expressions #167

We've had several people get confused by these (example 1, 2, 3). I think the main problem is that these are hard-coded string values that basically perform magic under the covers and the documentation is hard-to-find. Would be nice if we could add some Intellisense or helper methods to make it easier to understand.

Example binding expression:

const blobOutput = output.storageBlob({
  connection: "AzureWebJobsStorage",
  path: "helloworld/{DateTime:MM-dd-yyyy H:mm:ss}.json",
});

Example route parameter:

app.http('httpTrigger1', {
    methods: ['GET', 'POST'],
    authLevel: 'anonymous',
    route: 'httpTrigger1/{id}',
    handler: httpTrigger1
});