By default, do not halt on BRK (#14)

This change introduces a new command line flag, '-b', that cause the
simulator to halt on the `BRK` instruction. By default, however, the
simulator will no longer halt on `BRK`.

As before, this behavior can be toggled in the preferences at run-time.

src/main/java/com/loomcom/symon/ui/PreferencesDialog.java

@@ -42,11 +42,11 @@ public class PreferencesDialog extends Observable implements Preferences {
     private JTextField programLoadAddressField;
 
     private int programLoadAddress = DEFAULT_PROGRAM_LOAD_ADDRESS;
-    private boolean haltOnBreak = DEFAULT_HALT_ON_BREAK;
+    private boolean haltOnBreak;
 
-    public PreferencesDialog(Frame parent, boolean modal) {
+    public PreferencesDialog(Frame parent, boolean modal, boolean haltOnBreak) {
         this.dialog = new JDialog(parent, modal);
-
+        this.haltOnBreak = haltOnBreak;
         createUi();
         updateUi();
     }