modify transfer to send/receive arbitrary bytes
general format and tidy up
take sequences as input to transfer
commit changes to spi.c
Merge pull request #1 from intrinseca/master

Merged SPI changes, still need to change it so that it returns some values. Would have preferred to merge into tpdev branch but I'll whip up a fix quickly. Sorry to anyone who tries to use this in the next 20 mins.