ivory-bsp-stm32f4: spi driver rounded out, but not tested (need tower scaffolding)
ivory.mk: support trevor's changes to ivory codegen options parser
UARTTower: greeting is parameterized
ivory-bsp-stm32f4: more work on SPI driver
ivory-bsp-stm32f4: SPI Driver in Tower seems to kinda work

* at least, it doesn't throw any of the particular errors I am
  checking for
* need to refactor a bunch to support easier testing, printing
  results, etc...