docs: Remove General Iterative file listing from SC/21's appendix.
docs: Add FITS conversion appendix to SC/21.

The bones of this were produced by Holly, and I've fleshed it out.
and added cross-reference definitions too.
docs: Remove a \small in a caption affecting subsequent html text in SC/21.
docs: Restore a \newpage in the appendix of SC/21.

This got lost from 463f2f06de14c when I struggled with git add -p
to exclude a long section contiguous to it.  It's needed to prevent
the text in the following section to be interspersed with the
table split over three pages in the PDF.
docs: Rewrite and add headings to masking sections of SC/21.
docs: Various changes to SC/21.

Formatting, typos, and text revisions and deletions.
docs: Change PICARD recipe name in SC/21.

MOSAIC_JCMT_IMMAGES -> MOSAIC_SCUBA2_IMAGES
docs: Move the figures in Section 6 of SC/21.

The aim is to get them to appear in their own sections, with suitable
magnfication.  The ones in displaying mask won't scale to requested
height in the html, so keep with the one \myfig for each, rather than
separate scalings for PDF and HTML.  The positions and location
directives  may change if the document layout is otherwise adjusted.

Used \myfig macro for some recent graphics.

Tidy a caption or two.
docs: Correct a misccellany of mostly typographical errors in SC/21.

It's mostly things I noticed while looking at the positions of the
figures, stuff like missing or wrong macros like drrecipe, misplaced
closing brace, dealing with a bad line wrap, more space between text
and a graphic in HTML.
docs: Try a different \gaiathing definition in SC/21.

To match the GAIA style better make the gaiathing a bold  san serif
fount.  It's looks fine in the PDF, but the html it's bold italic roman.
Still on one page that had too much bold from a TIP as well as several
GAIA things, the italics delineate the two.  We shall have to see if
Holly approves this change.
docs: Add a "Flattening the background" heading and text to SC/21.
docs: Coloured quotes for example commands and output in SC/21.

Holly's change didn't work well in HTML, where early on the quotes
switched to black and the main text was in MidnighrtBlue.  I tried
adding a \color{Black} to restore the normal black text, but that only
succeeding in making the examples green.  Until the HTML aspect is
robust I have added a \renewcommand for HTML to retain the normal
myquote environment.  I would have bracketed the original definition
with htmlonly/latexonly but the point where newenviroments are supposed
to go comes before those are defined.
docs: Holly wants Chapters in SC/21.
docs: Strive for consistency in titles in SC/21.

Standardised the capitalisation styles: uppercase for each non-trivial
word in chapters, but only capitals for the first word (except for
names) in the sections and appendices.

Make the section and chapter names in links match the actual titles.

Apply \texttt and \drrecipe wrapper to the file and recipes names
respectively in titles.
docs: Another miscellany of corrections to SC/21.

Wrapped some new text to be visible in the editor.

Added some missed \gaiathing wrappers.

Commented out the sentence that has a reference to sec:jk, which no
longer exists.  It can be deleted once it's confirmed that it's not
being replaced, or should point to a different section.
docs: Compress the gap in the troubleshooting table of SC/21.
docs: Remove JAC document no longer referenced in SC/21.