[NES II] Read and display the catalog from an Apple DOS 3.3-compatible disk

[JMarlin]

Description

In the ultimate goal of creating some kind of minimal DOS for the NES, it is my intent to use the Apple DOS 3.3 filing system in order to achieve interoperability with my apples and maybe make a move to developing NOS applications on them.

To this end, I want to start by adding a demo command to the current NOS command interpreter that can navigate the FS hierarchy and produce a listing of all the files stored on the disk.

Acceptance criteria

• [x] Read and dump the VTOC sector off an Apple DOS disk
• [x] Update seek subroutine to allow for backward stepping so that we can read arbitrary sectors out-of-order
• [x] Use VTOC sector to read and dump the first catalog sector
• [x] Step through chain of catalog sectors and calculate a total count of catalog sectors and files
• [x] Print file names in catalog entries during catalog step-through

[JMarlin]

Getting very close, I'm now able to iterate through all of the catalog sectors and print catalog entries. Now there just needs to be some cleanup, because I'm printing some blank entries that clearly shouldn't be showing up and some entries have garbage characters at the beginning for some reason.

[JMarlin]

This works perfectly fine now. Just had a bad offset into the file name strings and was printing a newline at the top of every catalog sector loop.

Gonna PR this thing and close this out.