* Adds an initial test for DOS format (.do) files
* Fix physical sector order when nibblizing DOS 3.3 ordered images
Before, when `.dsk` or `.do` images were nibblized, the resulting
track had the sectors in the wrong physical layout.
Now the nibblized track has the correct physical layout (all sectors
in order) which results in the correct DOS 3.3 layout as well.
There is also a test that verifies the order.
* Add another test for a non-zero sector
The new test checks that the values in physical sector 1 are those for
DOS sector 7.
* Add test for all physical sectors on all tracks
This change also removes a few stray console.log calls in the test.
