stm32l1 - basics of USART registers
stm32l1 - Added all control registers, implemented the initialization.
stm32l1 - improved the current frequency computation.
stm32l1 - implemented most of the clock configuration.
stm32l1 - MCO clock support
stm32l1 - improved clock configuration, completed HSI and MSI parts
stm32l1 - implemented RCC->CSR registers, bus frequency getters.
stm32l1 - enabled use of USART in the app_blink
stm32l1 - moved usart test code into a separate app
stm32l1 - implemented GPIO alternative functions, fixed USART baud rate and sync logic
Merge pull request #228 from kvark/usart-app

STM32L1 - USART and system clocks
stm32l1 - added the default clock configuration, cleaned up app_usart
stm32l1 - mapped SPI registers
stm32l1 - implemented SPI initialization, expanded I2S registers, fixed GPIO names format
stm32l1 - fixed Spi trait name and implemented it
Merge pull request #229 from kvark/spi

Added SPI support for STM32L1