TODO:
  - Move back to module based build system.
  - Make compression algorithm and speed/level selectable.
  - Create utilities for:
    - Resizing a compressed device.
    - Checking and repairing a compressed device.
  - Check parameters in compress_ctr:
    - Compressed device must be large enough.
    - Backing device must be large enough.
   - Remove workqueue.
  - (?) Write / flush once per second.  What about sync?
  - (?) Don't cache lblk_alloc.
  - (?) Function ptrs for reading and writing lblk_alloc.