- Added a generic `Operator` registry and implemented Operators for
dos3.3 and NakeOS/Super-Mon disks.
- Currently Operators implement only the `Catalog` command.
- Loading a .dsk (or any other file type) should yield a SectorMap
interface, which reads and writes *physical*
sectors. (Auto-detection of sector mapping will come later.)
- The various filesystem packages (dos33, supermon, etc.) are
responsible for logical sector mapping.
- The weird part about this is that .dsk images are already mapped to
dos33 logical sector order, so they have to be un-mapped, then
re-mapped by the dos33 package. It's still cleaner that way.
