docs maint: user guide: driver options are a bit difficult to maintain

[Lee Read]

I used a table to describe driver options.

This is a bit awkward:

• It is easy to get lost between option column and default column when editing
• There is no linkable heading for each opt

I think I'll restructure to not use a table.
Driver options will be linkable, show up in the table of contents, and doc will be easier to maintain.
The defaults will not be as easy to see at a glance, but I'll come up with a consistent visual convention.