Basic Lambda / node functionality

[peoplemerge]

Lambda app should respond to an s3 event that dir structure containing images has changed.

This guide explains the source and steps http://docs.aws.amazon.com/lambda/latest/dg/getting-started-amazons3-events.html and http://docs.aws.amazon.com/lambda/latest/dg/walkthrough-s3-events-adminuser.html

Expect the event to have the format http://docs.aws.amazon.com/AmazonS3/latest/dev/notification-content-structure.html but all you need is the bucket name (well maybe 1-2 more like region).

Write a metadata file in json that reflects the structure of the dir tree, in alphanumeric order. For example:
sculpture
sculpture/2_angel.jpg
sculpture/1_duck.jpg
paintings
paintings/1_amywinehouse.jpg

resulting json:

{
"categories": {
  "sculpture":[
    "1_duck.jpg",
    "2_angel.jpg"
  ], 
  "paintings":[
    "1_amywinehouse.jpg"
  ]
}
}

For now don't worry about the case when a user loads 1000 images. The script will run 1000 times, which is fine.
Write documentation on how a developer can set it up (bucket names / iam permissions), using http://docs.aws.amazon.com/lambda/latest/dg/getting-started-custom-events.html as a reference