functions & RTC IRQ handler implementation

[fpistm]

can we have at least a minimal example for active halt with RTC or interrupt wake up? i have tried to use the HAL example and it never wakes, besides the LCD is shut down, meaning its not in active halt, but in halt.

Originally posted by @0x0fe in https://github.com/stm32duino/Arduino_Core_STM8/issues/34#issuecomment-1288569972