Use equally sized figures for the different kinds of discrete-time va…

…riables

This is a preparation for having these side by side as subfigures, as the non-conforming layout of the old figures didn't look good at all with the graphics appearing so close together.

As a bonus, the new figures also come as SVG, which makes them crisp and scalable also in the LaTeXML build.

chapters/synchronous.tex

@@ -207,7 +207,7 @@ \subsection{Clocks and Clocked Variables}\doublelabel{clocks-and-clocked-variabl
 
 \begin{figure}[H]
   \begin{center}
-    \includegraphics[width=3in]{piecewise}
+    \includegraphics{piecewise-constant}
   \end{center}
   \caption{A piecewise-constant variable.}\doublelabel{fig:piecewise-constant-variable}
 \end{figure}
@@ -228,7 +228,7 @@ \subsection{Clocks and Clocked Variables}\doublelabel{clocks-and-clocked-variabl
 
 \begin{figure}[H]
   \begin{center}
-    \includegraphics[width=3in]{clock}
+    \includegraphics{clock}
   \end{center}
   \caption{A clock variable.  The value of a clock variable is not defined --- the plot marks only indicate \emph{when} the clock is active.}\doublelabel{fig:clock-variable}
 \end{figure}
@@ -244,7 +244,7 @@ \subsection{Clocks and Clocked Variables}\doublelabel{clocks-and-clocked-variabl
 
 \begin{figure}[H]
   \begin{center}
-    \includegraphics[width=3in]{clocked}
+    \includegraphics{clocked}
   \end{center}
   \caption{A clocked variable.  The \lstinline!hold! extrapolation of the value at the last event instant is illustrated with dashed green lines.}\doublelabel{fig:clocked-variable}
 \end{figure}