Fix for ImportError: /usr/local/lib/python<x>.<y>/dist-packages/hid.so: undefined symbol: libusb_open

...12 and Ubuntu 12.04. Thanks to Stéfan van der Walt's help on this.
Can be changed to the following code to support 64 or 32 bit system

```
import struct

if struct.calcsize("P") == 8:   # 64 bit
    os.environ['LDFLAGS'] = "-L/usr/lib/x86_64-linux-gnu -lusb-1.0 -ludev -lrt"
else:
    os.environ['LDFLAGS'] = "-L/usr/lib/i386-linux-gnu -lusb-1.0 -ludev -lrt"
```