Improve object file format documentation (#1010)

Replacing the big pre-formatted text block with a list brings:
- Better accessibility, obviously
- Responsiveness
- Better formatting (bold, etc.)
- Sub-sections that can now be linked to
- Hyperlink cross-refs to other pages

The slight disadvantage is that `ENDC` etc. are now individual
list items, whereas they'd be better as part of the same item.
No big deal though, it was much worse before.

Some descriptions have been overhauled for clarity, and some
outright corrected (such as Assertions' "Offset" field).

Co-authored-by: Antonio Vivace <[email protected]>