Fix day offset calculation

eg. If date1 = (2013,5,27,11,18) and date2 = (2013,5,29,3,15), pretty.date would show "tomorrow" instead of 2 days forward. Correct day delta is now calculated from dates, not datetimes.
Tech Debt: handle times less than 24 hours in hours instead of days
Tech Debt: flake8 and version bump