Added following failing spec FIRST

    context "#date_tomorrow" do
        it "returns tomorrow's date" do
            calendar = Calendar.new
            expect(calendar.date_tomorrow).to eql( (Time.now + Calendar::SECONDS_IN_ONE_DAY).day )
        end
    end

Then added the simplest implementation in Calendar class to pass the failing specs.

Also renamed the following private instance methods:
1. weekday_name_from_date 			WITH	weekday_name
2. week_day_number_from_date		WITH	weekday_number
3. day_number_in_month_from_date	WITH	monthday_number

Added new private instance method: tomorrow_datetime_object