Event Interrupt

This example demonstrates handeling an interrupt with a task. 

When the external INT1 is triggered, the EINT1 ISR routine sets the Task 3 event flag 
and clears the interrupt flag and quits, then task3 enters the ready state, because task3 has
the highest priority in the demo, so task3 will run immidately, works like in the ISR routine.

Task 1 and Task 2 are used to show the code is running

This method can be used to serve all the IRQ interrupt sources. The "interrupt" tasks can be 
assigned a priority as required by the software developer.