manual: use modified "haddock.theme" for nicer syntax highlighting;

use `tcolorbox` instead of `framed` for latex code blocks, works
  much better, especially as now when using a background colour;
  reduce gap after figures and force footnotes to bottom of page;
  move most symbology figures to after some text to lessen chance
  of subsection headers being orphaned on their own at end of page:
  required a number of rewordings;
  use named barcodes in example commands, rather than numbered;
  fix "lua-crossrefs" filter to allow parentheses around
  references;
  various other fixes and rephrasings

docs/inc_header_pdf.tex

@@ -18,18 +18,16 @@
     \ifx\tmp\@nnil\originalitem\else\originalitem[#1]\hfill\par\fi}
 \makeatother
 
-%% Text and background color for inline code
+%% Use the wonderful `tcolorbox` instead of `framed` for fenced code blocks
+\usepackage{tcolorbox}
+\tcbuselibrary{breakable}
+\renewenvironment{Shaded}{\begin{tcolorbox}[colframe=white,boxrule=0pt,boxsep=0.5mm,top=0mm,bottom=0mm,colback=shadecolor,breakable=true]}{\end{tcolorbox}}
+
+%% Text color for inline code
 \usepackage{xcolor}
-\definecolor{icfg}{HTML}{331a33}
+\definecolor{icfg}{HTML}{351c35} % "text-color" in modified "haddock.theme"
 \let\oldtexttt\texttt
 \renewcommand{\texttt}[1]{\textcolor{icfg}{\oldtexttt{#1}}}
-%% Unfortunately this messes up wrapping TODO: fix
-%% Background color for inline code https://tex.stackexchange.com/a/507116
-%\definecolor{icbg}{HTML}{fafafa} % Same as modified pygments.theme
-%\newcommand{\code}[1]{%
-    %\begingroup\setlength{\fboxsep}{1pt}
-    %\colorbox{icbg}{\oldtexttt{\hspace*{0.1pt}\vphantom{A}#1\hspace*{0.1pt}}}\endgroup}
-%\renewcommand{\texttt}[1]{\textcolor{icfg}{\code{\oldtexttt{#1}}}}
 
 %% Make level-4 headings standalone (not run-in) - for some reason "-V block-headings" doesn't seem to work, so do
 %% what it does manually here
@@ -39,5 +37,9 @@
 %% PDF metadata - the values are set in "docs/inc_before_body_pdf.tex" (otherwise may get overridden)
 \usepackage{hyperref}
 
-%% pandoc-lua-crossrefs: required package
+%% Reduce gap after figures
 \usepackage{caption}
+\captionsetup[figure]{belowskip=-6pt}
+
+%% Make footnotes go to bottom of page
+\usepackage[bottom]{footmisc}