* Updated stm32f0 to 0.6.0 and neatened other deps
* Adjusted names and removed unneeded unsafe blocks
* Overhauled RCC to gate HSI48 correctly and add a selector function for it to CFGR
* Makes use of Rcc parameters rather than making RCC pointers
* Applys CS parameters to GPIO functions that mutate the port non
atomically
* Cut down on build gating hell a bit
* Add GPIO support for the stm32f091
* Implement RCC, Serial and Timers for stm32f091
* Implement ADC, I2C and SPI for stm32f091
* Add STM32F091 to Travis config, CHANGELOG and README
Base implementation of ADC functionality according to the embedded hal
traits for `Channel` and `OneShot`. Also provides references for
converting the internal temperature sensor and voltage reference values,
also the VBat reference where available.
Closes#11.
Daniel Egger