Start adding timers

[martinberlin]

Check #1
The idea of this PR is to add Timers and Alarm support so we can get INT low (interrupt pin) and also use this RTC for other meaningful things than maintain time (For that is better DS3231)

Reference libraries

• https://github.com/HausnerR/AVR-PCF8563/blob/master/PCF8563.c
• https://github.com/lewisxhe/PCF8563_Library/tree/master/src note: I don’t trust this library at this point and it’s doing unnecessary read operations that are not really needed. The AVR source looks more appropriate