Add .gitattributes in order to control LF normalization.
Add vim's .swp files to .gitignore.
TIMER: First instance of a timer driver with a suitable function set and PWM functionality.
TIMER: Add countdown functionality with 1ms resolution.
TIMER: Add a stopwatch feature.
TIMER: Stop the timer for oneshots directly in the ISR.

- Tests have shown that the oneshot can be stopped within 50 system clock
cycles after the interrupt has been triggered.

- TIMER_GetClockPrescalerValue() becomes a public function.
TIMER: Add an interactive (CMDL) test set.
TIMER: bugfixes and enhancements.
RUNLOOP: Initial version of the RUNLOOP subsystem.
RUNLOOP: Add debug prints.
RUNLOOP: Add test application.
TIMER: Add new feature: TIMER_SetStopwatchTimeCallback(). Code optimization.
RUNLOOP: Let the runloop internally count system clock cycles instead of milliseconds.

In order to improve timing precision, the RUNLOOP makes use of the
TIMER's stopwatch instead of the TIMER's countdown. This allows to
make use of a continuously running timer, which also eliminates time drifts.
RUNLOOP: Adjust the runloop-test for changes in the RUNLOOP subsystem.
RUNLOOP: Introduce taskStateReady as an intermediate task state between taskStateNew and taskStateActive.

This fixes a potential overflow error while maintaining the order of execution after adding new tasks.
RUNLOOP: Allow to adjust the timer clock prescaler during initialization. Add support for error callbacks.

The runloop subsystem now allows to register a task error callback and a synchronization error callback.
The first is executed if a task returns with an error code other than RUNLOOP_OK or RUNLOOP_OK_TASK_ABORT.
The latter is executed if the execution time of a task delays another task by more than its execution period.
In this situation, the runloop drops task executions.
RUNLOOP: Add error callbacks to test application.
UART: More explicit behavior on writeRxToBuffer option for rx callbacks. Optimized code for the case that no rx callbacks are needed.
A few code comments.
UART: Optimization on UART_TxByte() and UART_RxByte().