* Build containers from scratch for more accurate testing.
* Allow environment load to be skipped.
* Allow bash wrapping to be skipped.
* Allow forcing a command to run as a user without sudo.
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.)
* Make the code more modular and object-oriented.
* Multiple Docker containers can now be created for a single test to simulate more realistic environments.