Updates to Spipy

Hi Tom,

I'm currently working on integrating a custom board onto the RPi for my final year project at Cambridge, and your library is the most functional Python SPI library I've seen yet.

I've forked it and made some changes to the transfer function to make it more 'generic' and I changed the module name to avoid a clash with one of the other python modules I'd installed that I didn't want to find and delete.

I'd love to work with you to improve this module and I'm happy to rework my changes to a less api-breaking form, this was just all I needed to get my board up and running.

Kind Regards,

Michael Allan
mda39@cam.ac.uk