Start adding STM32F4 cmsis and placeholders for the C API
Add nvic dynamic vector handling.
Add STM32 to the buildchain
Add alternative function to pinmap for STM32.
Add untested port api
Add analog in api
Add GPIO api
Add I2C master mode API
Add SPI api
Add pinmap.
Add define to let stm32f4xx.h know which uC version we are working with.
Add device specific pin definitions, etc.
Add options.json file for STM32.
Lots of small changes which get us compiling.
Add us_ticker api.
Lot of small fixes to cmsis code so it works correctly.
Remove moved options file.
Generate update event when initializing the ticker so the new prescaler
value is used straight away.
Small fixes to the GPIO api, meaning it works!
Make pinmap and port API use the correct memory region for the GPIOs.