* Combine hardlink and non/compressed in synthetic tests to reduce test time and improve coverage.
* Change log level of hardlink logging to detail.
* Cast size in S3 manifest to integer.
Refactor storage layer to allow for new repository filesystems using drivers. (Reviewed by Cynthia Shang.)
Refactor IO layer to allow for new compression formats, checksum types, and other capabilities using filters. (Reviewed by Cynthia Shang.)
