every X days should run on the same day if the At() time has yet to come

[JohnRoesler]

What does this do?

• currently 7am, run a schedule for every 2 days at 9am and 11am -> should run at 9am and 11am on the day the scheduler was started
• currently 12 noon, run a schedule for every 2 days at 9am and 11am -> should run at 9am and 11am two days after the scheduler started

Which issue(s) does this PR fix/relate to?

resolves #552

List any changes that modify/break current functionality

The initial scheduling of jobs using At time changed to be more intuitive (see the description above)

Have you included tests for your changes?

Did you document any new/modified functionality?

• Updated example_test.go
• Updated README.md

Notes