Provide an API for creating AMIs

Bug Description
Currently, to create an AMI, you need to do the following:
 1) create an image (e.g., create an image from an existing machine)
 2) create a bundle of an image
 3) create a bucket on S3
 4) upload the bundle (and the manifest file that was created during the bundling)

At this point, one can register this AMI for use by EC2.

Support for step #3 already exists in txAWS and should just be done automatically in an txAWS upload call.

What would be nice is to provide an API for programmers such that these steps could be performed by making AWS calls via txAWS. A programmer could then write a script that goes from image-creation all the way through AMI registration and instance startup.

References:
 * http://docs.amazonwebservices.com/AmazonEC2/dg/2006-06-26/bundling-an-ami.html