DS3231 library for AVR.
  
  This fork has been created to support AVR devices with USI interface.

  This library implements the following features:

   - read/write of current time, both of the alarms,
   control/status registers, aging register
   - read of the temperature register, and of any address from the chip.
   
   To use this library two additional libraries have to be used:
   Millis library: https://github.com/Tekl7/Millis
   USIWire library: https://github.com/puuu/USIWire

  Author:          Petre Rodan <2b4eda@subdimension.ro>, Vojtěch Tecl
  Available from:  https://github.com/Tekl7/ds3231
  License:         GNU GPLv3

  The DS3231 is a low-cost, extremely accurate I2C real-time clock 
  (RTC) with an integrated temperature-compensated crystal oscillator 
  (TCXO) and crystal.