Add style for QPushButton:checked

and update example

Fix #26

example/example_pyside.py

@@ -32,7 +32,7 @@ Requirements:
     - Python 2 or Python 3
     - PySide
 
-.. note.. :: qdarkstyle does not have to be installed to run 
+.. note.. :: qdarkstyle does not have to be installed to run
     the example
 
 """
@@ -55,7 +55,7 @@ def main():
     # create the application and the main window
     app = QtGui.QApplication(sys.argv)
     window = QtGui.QMainWindow()
-    
+
     # setup ui
     ui = example_ui.Ui_MainWindow()
     ui.setupUi(window)
@@ -79,7 +79,7 @@ def main():
     # setup stylesheet
     app.setStyleSheet(qdarkstyle.load_stylesheet(pyside=True))
 
-        # auto quit after 2s when testing on travis-ci
+    # auto quit after 2s when testing on travis-ci
     if "--travis" in sys.argv:
         QtCore.QTimer.singleShot(2000, app.exit)
 
@@ -90,4 +90,3 @@ def main():
 
 if __name__ == "__main__":
     main()
-