[time.clock.req] Make list item end with comma, not full stop.

Also reformat the itemization source to be more edit-friendly.

Author: tkoeppe

source/time.tex

@@ -1012,22 +1012,24 @@
 \pnum
 A type \tcode{TC} meets the \oldconcept{TrivialClock} requirements if:
 \begin{itemize}
-\item \tcode{TC} meets the \oldconcept{Clock} requirements,
+\item
+\tcode{TC} meets the \oldconcept{Clock} requirements,
 
-\item the types \tcode{TC::rep}, \tcode{TC::duration}, and \tcode{TC::time_point}
+\item
+the types \tcode{TC::rep}, \tcode{TC::duration}, and \tcode{TC::time_point}
 meet the \oldconcept{EqualityComparable} (\tref{cpp17.equalitycomparable}) and
 \oldconcept{LessThanComparable} (\tref{cpp17.lessthancomparable})
 and \oldconcept{Swappable}\iref{swappable.requirements}
 requirements and the requirements of
-numeric types\iref{numeric.requirements}.
+numeric types\iref{numeric.requirements},
 \begin{note}
 This means, in particular,
 that operations on these types will not throw exceptions.
 \end{note}
-
-\item the function \tcode{TC::now()} does not throw exceptions, and
-
-\item the type \tcode{TC::time_point::clock} meets the \oldconcept{TrivialClock}
+\item
+the function \tcode{TC::now()} does not throw exceptions, and
+\item
+the type \tcode{TC::time_point::clock} meets the \oldconcept{TrivialClock}
 requirements, recursively.
 \end{itemize}