First shot at Amazon Glacier support.

short summary:
* working: configuration, storing in Glacier files not larger than 10GB (constant chunk size)
* code and specs based heavily off S3 implementation
* #nearest_power_of_two method and file-size checking ready for implementing chunk size calculation
* not implemented: removing archives (used for cycling/keep)
update dependencies
allow Storages to store package metadata
Glacier updates

- use multipart upload for files larger than +chunk_size+
- retry failed requests
- store AWS `archive_id` in YAML file for cycling