bma250 SPI module for u3, u6, ue9 and usage example

I noticed there wasn't an example for using SPI, so I put a basic one together.  The example script only uses u6 right now because that's all I had to test.  The bma250 module should work on u3 and ue9 as well but it needs testing.  Thought someone might find this useful!  Let me know if there's any changes you'd like to see to this before it's merged.