[algorithms.parallel.defns] New paragraph for example (#6447)

Making the example a sibling to the preceding paragraph
rather than part of it resets its list numbering, which is less
confusing than continuing numbering.

Author: AlisdairM

source/algorithms.tex

@@ -312,6 +312,8 @@
 \end{note}
 \end{itemize}
 These functions are herein called \defn{element access functions}.
+
+\pnum
 \begin{example}
 The \tcode{sort} function may invoke the following element access functions:
 \begin{itemize}