Use filename for NDF structure diagram that is more general
Minor cleanups of NDF structure diagram

- Fix line widths to be consistent
- Tweak offset of text from line
Replace hdstrace of historical models with diagrams

Referee #1 did not like the hdstrace output.
Can no longer refer to "above trace"
Add VARIANT and EXTEND_SIZE to HISTORY
Replace "modern" Asterix trace with diagram
Tweak layout of table example