Update examples (to run with "python" or "pytest")

Author: mdmintz

examples/handle_alert_test.py

@@ -1,4 +1,5 @@
 from seleniumbase import BaseCase
+BaseCase.main(__name__, __file__)
 
 
 class HandleAlertTests(BaseCase):

examples/nth_child_test.py

@@ -1,4 +1,5 @@
 from seleniumbase import BaseCase
+BaseCase.main(__name__, __file__)
 
 
 class NthChildSelectorTests(BaseCase):

examples/test_double_click.py

@@ -1,5 +1,6 @@
 """Test double_click() after switching into iframes."""
 from seleniumbase import BaseCase
+BaseCase.main(__name__, __file__)
 
 
 class DoubleClickTests(BaseCase):

examples/test_iframes.py

@@ -1,5 +1,6 @@
 """Use SeleniumBase methods to interact with iframes."""
 from seleniumbase import BaseCase
+BaseCase.main(__name__, __file__)
 
 
 class FrameTests(BaseCase):

examples/test_window_switching.py

@@ -4,6 +4,7 @@
 The starting window is window(0). Then increments by 1.
 """
 from seleniumbase import BaseCase
+BaseCase.main(__name__, __file__)
 
 
 class TabSwitchingTests(BaseCase):