Clean up fstat.1

Clean up fstat.1

- Sort options in the list & indent for readability.
- Pet linters
  - Use "\(em" instead of "--"
  - Remove Tn macros
- Use Ql instead of Dq Li
- Add arguments to the -M, -N, -p, and -u options in their descriptions.
- Use Sy instead of Li for field names. Li is deprecated, and Ql makes no
  sense here.
- Replace a literal block with a list for the table of special names
  related to FD.
- Use Ql instead of ``X''.
- Add a dot after etc.
- Reference fuser(1).

MFC after:	1 week