Update imager-example.js

storageClass parameter added to S3 configuration, allow to choose between STANDARD and REDUCED_REDUNDANCY (REDUCED_REDUNDANCY is cheaper ;))
Update imager.js

storageClass parameter added for S3 to choose between STANDARD and REDUCED_REDUNDANCY storage (REDUCED_REDUNDANCY is cheaper ;))
Merge pull request #29 from zefranck/master

"x-amz-storage-class" added to use cheaper S3 hosting if needed