implement calendarWeeks option
it prepends a .cw cell to each row and displays the current calendar week before the first day of the week
defaults weekStart to monday
specs and basic styling included
Use better algorithm for calendarWeeks, don't use calendarWeeks in weekStart's definition
Adjust today button width when calendarWeeks is set
Tweak calendar weeks styles
Use standard option-extraction code for calendarWeeks option
Document calendarWeeks option