HSI disabled.
Const param in clock
STM32: UartHAL: Provides a low level interface to Uart IP
STM32: UartHAL: Restructured initialization

setBaudrate used to do all the initialization.
The code for clock initialization has been moved to an enable/disable
method (similar to the Timer peripheral).
The constructor was replaced by an initialize function because
there is no need for instanciating this class.
The initialize function basically handles what used to be done
by the setBausrate function.
setBaudrate now only does what it says it does: setting the Baudrate.
STM32: UartHAL: Can only reset certain flags.
STM32: UartHAL: Make enums public
STM32: UartHAL: Parity can only be set while UART is disabled.
STM32: UartHAL: setParity: change datat mode to 9bit

Parity bit counts as additional data bit.
STM32: UartHAL: use Enumclass instead of enum
STM32: UartHAL: Added docu. Fixed parity disable.
STM32: UartHAL: Overflow interrupt flag added
UartHAL: Make compile for F4
STM32: UartHAL: Moved enums to common base class.
Examples: STM32F3D: Added Simple UartHal Example
Examples: STM32F3D: UartHal: Now sends in an interrupt.
Merge branch 'feature/uart_hal_rebase' into develop

feature/uart_hal_rebase contains all changes made on
feature/uart_hal in a rabased fashion.
Therefore this commit makes the feature/uart_hal
branch obsolete.