Use table to present extended BNF

This is similar to how we present string escape sequences, with good formatting of the textual descriptions.

chapters/syntax.tex

@@ -2,12 +2,19 @@ \chapter{Modelica Concrete Syntax}\label{modelica-concrete-syntax}
 \section{Lexical conventions}\label{lexical-conventions}
 
 The following syntactic meta symbols are used (extended BNF):
-\begin{lstlisting}[language=grammar]
-[ ] optional
-{ } repeat zero or more times
-| or
-"text" The text is treated as a single token (no white-space between any characters)
-\end{lstlisting}
+\begin{center}
+\begin{tabular}{c l}
+\hline
+\tablehead{Syntax} & \tablehead{Description}\\
+\hline
+\hline
+\lstinline[language=grammar]![ $\ldots$ ]! & Optional\\
+\lstinline[language=grammar]!{ $\ldots$ }! & Repeat zero or more times\\
+\lstinline[language=grammar]!$\ldots$ | $\ldots$! & Alternatives\\
+\lstinline[language=grammar]!"$\mathit{text}$"! & The $\mathit{text}$ is treated as a single token (no white-space between any characters)\\
+\hline
+\end{tabular}
+\end{center}
 
 The following lexical units are defined (the ones in boldface are the
 ones used in the grammar, the rest are just internal to the definition