Support Raspbian Stretch

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Many things need changing for Stretch, so far:

• ds3231_setup

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Confirmed ds3231_setup is broken even with NTP installed. It "works" but the RTC gets set to an insane time every boot, about 1 year in the past.

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This URL has working instructions for getting an RTC to work with Stretch, except missing the removal of fake hwclock:

https://www.raspberrypi.org/forums/viewtopic.php?f=66&t=85683&sid=49e60d355390530233ab9ee33896f2e4&start=50

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https://wiki.archlinux.org/index.php/systemd-timesyncd