Remove RC3ChanJoystickController or add related sketch

[Ezward]

The RC3ChanJoystickController and RC3ChanJoystick in controllers.py appear to be abandoned code. It lookes like they provide a Linux device at /dev/input/js0 for a standard 3 channnel RC controller. However there is no other code to implement this. I assume there is a sketch that uses a Teensy or other Arduino compatible the emulate a HID device over USB, but there is not reference to such a sketch. If we can add the sketch to our repo OR have a link to the sketch in another open source repo then we can reference it in the code and in the docs. Otherwise we should remove this code.

@n6wxd I see you added the code. However it does not appear to be useful by itself. Is there an arduino sketch that should be used with it? Are there any other docs on how to use this part?

[n6wxd]

This code was added used to interface a RC Throttle Controller to a RC Receiver connected via USB to the DC. The UCSD group used this type of controller to train with. You can find the Teensy code at my public repo: https://github.com/n6wxd/wireless-rc-adapter

[Ezward]

@n6wxd Fantastic. I'll add this to the docs. Thanks.

[Ezward]

I've update the docs to include a reference to the sketch and the wiki on how to wire up the microcontroller to the receiver. I think this is now a viable option for users.