it's just an ATmega328P, it should be directly compatible with whatever library you throw at it as long as it doesn't occupy the USB D+ and D- pins.
and also the schematic http://www.circuitsathome.com/chome_downloads/UHS_mini_10.pdf
, pay special attention to pin mapping
The SPI signals are obvious
As the webpage said, INT goes to pin 9 (meaning PB1)
Now you should be able to figure out how to wire it all up. The MAX_RST signal can go to any unused pin on the ATmega328P, I suggest you perform a reset of the MAX3421 upon resetting the ATmega328P just because it'll ensure that your firmware starts from a fresh state every time.
Set USnooBie to run at 3.3V using the jumper
The 5V pin from USnooBie is still available and you need to connect that to "RAW" on the USB host shield. Also read their site where it says
Mini shield lacks flexibility of its full size brother; however, here is one simple way to get 5V to VBUS using Arduino Pro Mini’s 3.3V on-board LDO. Power the board with 5V on RAW pin, cut the trace inside VBUS jumper, provide 5V from RAW to VBUS and get 3.3V from Arduino to the shield in the usual manner via 3.3V pin. While making this mod be extra careful and don’t short VBUS pad to USB connector shield. Also, this mod is easier to make when Arduino board is placed beneath the shield. Picture on the left shows necessary wiring.