Merge pull request #3 from j-eggi/main

Renamed screenshot files to all have lowercase .png extension

Author: Foadsf

Pictures/pic4_NX_message_box.PNG renamed to Pictures/pic4_NX_message_box.png

@@ -106,11 +106,9 @@ if __name__ == '__main__':
 
 and the result must be
 
-pic6_NX_information_window
-
 <pre>
   <center>
     <img src=".\\Pictures\\pic6_NX_information_window.png" width="500">
     <figcaption>Fig.6 - Information box window.</figcaption>
   </center>                  
-</pre>
+</pre>