Adding in S3 Loader/Storage/Result Storage

Have also added in the necessary config settings to thumbor.conf and config.py

Have taken code from some extensions I wrote to provide this functionality. You can see them at https://github.com/willtrking/thumbor_aws

These extensions are going to be used in production at upout.com very soon

Required python packages:
boto (all)
python-dateutil (storage/result_storage provides expiration functionality)

BUG IN BOTO
When the first character of a key name is a / boto will generate invalid signing keys with suppress_consec_slashes=False

Other bugs fixed:

The put_detector function in storages.file_storage did not correctly check for directory existence.