When running `make epub`, Make would try to satisfy the target
'src/plfa/acknowledgements_epub.md' by calling run-liquid.lua. But due
to the use of shell redirection, Make would always create the file
acknowledgements_epub.md, even if run-liquid.lua failed, in which case
acknowledgements_epub.md would be empty. This empty file would still
satisfy the 'src/plfa/acknowledgements_epub.md' target, allowing the
pandoc command line in the 'out/plfa.epub' target to proceed---and later
fail.
To avoid this, we now (a) add a bunch of error checking to run-liquid.lua,
and (b) write directly to acknowledgements_epub.md instead of relying on
shell redirection, so that acknowledgements_epub.md will only be created
(or modified) if run-liquid.lua succeeds.
HTML does not permit nested <p> elements, which epubcheck complains
about. This change fixes those remaining warnings.
This change also causes the Dedication on the website to be centered
when viewed in Safari, which it was not before. The EPUB output looks
the same in either version with Thorium reader 1.3 on macOS.
Use liquid-lua to generate acknowledgements_epub.md, which is used by
pandoc to build the EPUB book. Also stop using the '{%-' / '-%}'
syntax, which liquid-lua does not support, in templates.
Also add a vertical space between the first bullet in each bulleted
list so pandoc recognizes bulleted lists as such. This has no effect on
the the website.
