v.6.8.0 - 12/24h, improvements and bugfixes ( #27 ): PR #35 - Thanks to @pk17r

Here is some more functionality and bug corrections:

• I2C communication blocking bug in enableBattery() and disableBattery() mostly hitting on ESP32 and sometimes on Atmega328p. enableBattery() not always working bug. Closes #27
• addition of 12 hour / 24 hour clock mode select functionality
• flag to know if clock is in 12 hour / 24 hour mode and also AM-PM if in 12 hour mode
• added 12-24 hour mode select comment on example; a print statement that'll print AM-PM if in 12 hour mode
• model check before accessing SRAM or alarms, refresh() needs to be called before calling lostPower()
• bug correction on eosc flag, introduced in my last commit
• bug correction on not noting alarmClearFlag while clearing alarm flags, introduced in my last commit
• tabs replace spaces, introduced in my last commit
• tested all functionalities on Atmega328p and ESP32.

That's it! Thank you!

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This release (and previous one) is 100% by @pk17r . Thank you!