Option to display calendar week numbers

[michael-zock]

Are there any plans to add calendar week numbers, like the option "calendarWeeks" in the related https://github.com/eternicode/bootstrap-datepicker fork?

Use the demo on http://eternicode.github.io/bootstrap-datepicker/?markup=input&format=&weekStart=&startDate=&endDate=&startView=0&minViewMode=0&todayBtn=linked&language=en&orientation=auto&calendarWeeks=on&autoclose=on&todayHighlight=on&keyboardNavigation=on&forceParse=on#sandbox and look to the left of the day numbers to see what I'm talking about.

[nikoskalogridis]

implemented on v4 branch might as well be included on v3 with #478

[michael-zock]

Thanks!