USB to USB keyboard protocol converter
======================================
Hardware requirement
--------------------
Arduino Leonardo
    http://arduino.cc/en/Main/ArduinoBoardLeonardo 
Circuit@Home USB Host Shield 2.0
    http://www.circuitsathome.com/products-page/arduino-shields/usb-host-shield-2-0-for-arduino
Build firmware
--------------
    $ git clone git://github.com/tmk/tmk_keyboard.git
    $ cd tmk_keyboard
    $ git submodule init
    $ git submodule update
    $ cd converter/usb_usb
    $ make
You will get usb_usb.hex if you are lucky.
Program your Leonardo with avrdude(or easy-going Arduino IDE):
    $ avrdude -patmega32u4 -cavr109 -PCOM17 -b57600 -Uflash:w:usb_usb.hex
Limitation
----------
Only supports 'HID Boot protocol'.
Not support keyboard LED yet.