RTCZero

Adding Barrier instruction to standbyMode to prevent hangs after sleep as per this pull request: https://github.com/arduino-libraries/RTCZero/pull/42/commits/f2d8483770a279a77909d4eb4466a910849ad106

Calling setEpoch causes serial data to be lost. This is because the CLOCK register is altered bit by bit sequentially without the SYNCBUSY bit being checked with each update.

Release 1.5.3

Merge tag '1.5.2'

Merge pull request #38 from per1234/keywords-separator