Update checklist with HTML progress
Fix chapter headings

Only one set of <h_> markers for each chapter, use css to make the
subheading smaller.
Format end adverts.
Tidy up unused images
Update checklist.
No transcriber's note needed for this version of this book
Use full title
Cover image.
Orphaned markup check
No project notes to resolve.
No remaining notes to resolve
No allcaps smallcaps in this project
Fix tidy errors
No accessibility or link issues.
Remove unused CSS
Validation passes
No fixes to apply
All HTML checks complete.
Finished!