Displays a table of fonts for a give font number (first argument)
  in the current graphics terminal, e.g.:
\gdlcodeexample{showfont_3}{showfont}{}
\gdlcodeexample{showfont_4}{showfont}{}
\gdlcodeexample{showfont_5}{showfont}{}
\gdlcodeexample{showfont_6}{showfont}{}
\gdlcodeexample{showfont_7}{showfont}{}
\gdlcodeexample{showfont_8}{showfont}{}
\gdlcodeexample{showfont_9}{showfont}{}
\gdlcodeexample{showfont_11}{showfont}{}
\gdlcodeexample{showfont_12}{showfont}{}
\gdlcodeexample{showfont_13}{showfont}{}
\gdlcodeexample{showfont_14}{showfont}{}
\gdlcodeexample{showfont_15}{showfont}{}
\gdlcodeexample{showfont_16}{showfont}{}
\gdlcodeexample{showfont_17}{showfont}{}
\gdlcodeexample{showfont_18}{showfont}{}
\gdlcodeexample{showfont_20}{showfont}{}
