Support for pandoc 2.19.2

Previous I had been using pandoc 2.9.2.1, available through the Debian
repositories.  I installed 2.19.2 through Guix.

The biggest issue I ran into was wrapping of the output, which messed up
my klugy post-processing scripts that expected `h1` tags to have their
attributes all on the same line.  The `--wrap none` flag resolves that.

I diff'd the webroot before and after these changes.  The primary
changes were related to footnote classes, the recognition of fancy
quotes in a couple new situations, and new classes introduced to source
code listings.  I'll have to investigate styling them, since I haven't
visited the CSS for that in quite some time.

src/h12title

@@ -36,9 +36,15 @@ main()
       | grep '<h1' \
       | head -n1 \
       | grep -oP '(?<=>)[^<]+' \
-  )
+  ) || {
+    echo 'error: h12title: failed to locate heading' >&2
+    exit 1
+  }
 
-  sed "s#$placeholder#${title/&/\\&}#" <<< "$body"
+  sed "s#$placeholder#${title/&/\\&}#" <<< "$body" || {
+    printf "error: h12title: failed title replacement: '%s'\n" "$title" >&2
+    exit 1
+  }
 }
 
 main "$@"

src/post2html

@@ -135,7 +135,7 @@ main()
   pandoc -f"$( pexts )" -thtml5 \
          --standalone --template src/pandoc.tpl \
          --metadata pagetitle:ignoreme \
-         --base-header-level=1 \
+         --wrap none \
          -B <( src/mkheader post @__PAGE_TITLE__@ ) \
          -A src/footer.tpl.htm \
          < <( prefmt < "$file" ) \