Marketpress - Quantity of items in cart

Hi,
I've been searching but I cant find a simple way of displaying the quantity of items in the users cart in my page header.

Eg: You have 3 items in your cart

Your demo site shows it.

I know you can use mp_show_cart() to show all cart items but I am limited for space and I just want to show the total number of items in the users cart, and perhaps an empty cart link.

Thanks,
Mark