Added a GPIO implementation for the BeagleBoard target. Modified the test code to use the GPIO class for controlling LEDs, and also made the boot hang until the USER button is hit (to test capturing data from a GPIO pin).
Added a GPIO implementation for the BeagleBoard target. Modified the test code to use the GPIO class for controlling LEDs, and also made the boot hang until the USER button is hit (to test capturing data from a GPIO pin).

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