Implement the continue, continue_left, and continue_right options in the TikZ format.

This was an inconsistency between the two formats.  Basically, the
JSXGraph format did not honor the function max if `continue` or
`continue_right` was set, but the TikZ format did. This could result in
a function graph continuing to the right in the JSXGraph format, but not
in the TikZ format (assuming the board bounds go further to the right).
This just makes the TikZ output use the axes max instead of the function
max in this case.  Of course if `continue` and `continue_left` are set
then the axes min is used instead of the function min.

Author: drgrice1

lib/Plots/Tikz.pm

@@ -588,8 +588,11 @@ sub draw {
 				my $function = $data->function_string($f->{Fy}, 'PGF', $f->{xvar});
 				if ($function ne '') {
 					$data->update_min_max;
+					my ($axes_xmin, undef, $axes_xmax) = $plots->axes->bounds;
+					my $min = $data->style('continue') || $data->style('continue_left')  ? $axes_xmin : $f->{xmin};
+					my $max = $data->style('continue') || $data->style('continue_right') ? $axes_xmax : $f->{xmax};
 					$plot_options .= ", data cs=polar" if $data->style('polar');
-					$plot_options .= ", domain=$f->{xmin}:$f->{xmax}, samples=$f->{xsteps}";
+					$plot_options .= ", domain=$min:$max, samples=$f->{xsteps}";
 					$plot = "{$function}";
 				}
 			} else {