Support header/payload features in RestJson

Pull output keys from headers in RestJson and support root/payload
element keys in input and output.
Add min utility function
Refactor createHash function into util for use in Glacier
Support error response with code instead of __type (RestJson)
Extract request id from RestJson responses
Add support for Amazon Glacier (AWS.Glacier)
Add multi-part upload integration tests
Document Glacier.Client.computeChecksums
Document AWS_REGION environment variable in Examples guide
Remove AWS.util.min, use Math.min instead
Change integration test to upload parts concurrently (Glacier)
Add guide examples for Glacier archive uploads (single and multi-part)
Merge pull request #66 from aws/glacier

Add support for Amazon Glacier (AWS.Glacier)