Add API to check for left/right mouse events

convenience API to check for left/right mouse buttons on MouseEvents

src/de/gurkenlabs/litiengine/input/IMouse.java

@@ -255,6 +255,26 @@ public interface IMouse {
    */
   public boolean isRightButtonPressed();
 
+  /**
+   * Returns true if the mouse event specifies the left mouse button.
+   *
+   * @param event
+   *         The MouseEvent object
+   *
+   * @return true if the left mouse button was active.
+   */
+  public boolean isLeftButton(MouseEvent event);
+
+  /**
+   * Returns true if the mouse event specifies the right mouse button.
+   *
+   * @param event
+   *         The MouseEvent object
+   *
+   * @return true if the right mouse button was active.
+   */
+  public boolean isRightButton(MouseEvent event);
+
   /**
    * If set to true, the mouse will be locked to the render component of the game.
    * 

src/de/gurkenlabs/litiengine/input/Mouse.java

@@ -127,6 +127,16 @@ public boolean isRightButtonPressed() {
     return this.isRightMouseButtonDown;
   }
 
+  @Override
+  public boolean isLeftButton(MouseEvent event) {
+    return SwingUtilities.isLeftMouseButton(event);
+  }
+
+  @Override
+  public boolean isRightButton(MouseEvent event) {
+    return SwingUtilities.isRightMouseButton(event);
+  }
+
   @Override
   public void mouseClicked(final MouseEvent e) {
     this.updateLocation(e);