Support for DS1308 RTC

[OziPhil]

Hello Team

First let me thank you for such a great library.

Can I ask that support be added for the DS1308 RTC. It is very similar to the DS1307 except for bits 2..3 and 5..6 in the Control register. The RTC is interesting in that it allows you to set the SQW/CLKIN pin to input and then use synchronise with external clock source/1PPS from GPS to create a more accurate RTC.

Thanks in advance for your help.

Kind regards

Phil