bundle IDS citation style as ids.csl and make it the default

Include the IDS citation style (based on the style developed for
ICLC-10 2023 in Mannheim) as resources/ids.csl and pass it to pandoc
unless the document specifies a csl of its own. Drop the now-redundant
remote csl URL from examples/ids.Rmd.

Change-Id: Iaaff300bfb9d9b7ea80471b73de3bf6019fb9f93
diff --git a/man/revealjs_presentation.Rd b/man/revealjs_presentation.Rd
index ba10ef0..827370e 100644
--- a/man/revealjs_presentation.Rd
+++ b/man/revealjs_presentation.Rd
@@ -268,6 +268,14 @@
     toggleChalkboardButton: true
 }\if{html}{\out{</div>}}
 }
+
+\subsection{Bibliography and citations}{
+
+Documents with a \verb{bibliography:} in their YAML header are formatted with
+the bundled IDS citation style (\code{ids.csl}, based on the style developed
+for ICLC-10 2023 in Mannheim) by default. To use a different style,
+specify it as usual with \verb{csl:} in the YAML header.
+}
 }
 
 \examples{