Added Stationary-Base Demo and Updated README.md

This PR updates the README.md file to give usage info for the new stationary-base feature.
 
This PR also adds (and links to in the Readme) my stationary-joystick demo to your existing 2 joystick demos (basic and dual) that are already here.  I also created a new 'js' folder for my dependencies.  I went ahead and copied the new virtualjoystick.js from your Master and placed it here in the 'js' dependencies folder because my demo requires this updated version.  

Sorry I'm a little confused as to how hosting works on GitHub and which solution you are personally using for your demos.  I'm assuming that your demos and their dependencies are being hosted by your .github.io pages.  So I don't really know where the current demos are searching for their version of <src = 'virtualjoystick.js'. in their html files.  If I have misunderstood where to place the dependencies and how they are hosted for your demo pages, I will be glad to make any changes necessary.

Thanks!
-Erich