test the USB_Rx mechanism
delete unused code
add USB_Rx_STATUS and data pointer for controlling data readout process
add comment
point the pointer to data buffer
get rx data length and set data ready flag
define USB_RX_DRDY::USB Rx Data Ready; USB_RX_DNRDY::USB Rx Data Not Ready.
define USB_RX_DRDY::USB Rx Data Ready; USB_RX_DNRDY::USB Rx Data Not Ready.
define USB_RX_DRDY::USB Rx Data Ready; USB_RX_DNRDY::USB Rx Data Not Ready.
wait until user ready the USB Rx data, and clear the pointer and status
wait for data, after receive the data, all led blink one time
fix syntax error
clear Rx status
determine if data exisit
use bit operation instead of
directly define macro
Issue (1)
problem:     The original concept is using USB_RX_STATUS as the flag and variable to store receieve data length from USB Out endpoint.
	 Using while() to wait until main() read out data via pointer, and clear  USB_RX_STATUS for next receieve process.
             However, due to VCP_DataRx() function is called by USB_ISR interrupt, and therefore while() loop in main() has no priority to switch stack back into main(), so the thread is stock into while() loop in VCP_DataRx.