Support for LPTIM

[HalfSweet]

For some mcu's they come with LPTIM peripherals which are more flexible and lower power consumption than RTC for low power applications. will STM32LowPower library support LPTIM peripherals.

Maybe I can open a new pr, but this may require a new STM32RTC like dependency library, is there any coding specification required in this regard

[fpistm]

Hi @HalfSweet any contribution are welcome. I guess the first step would be to add the LPTIM in the PeripheralPins. I don't catch your point about a "new STM32RTC like dependency library"