Add day start week

[martell2010]

Hi, thanks for the work done. Can you add an option for specifying the first day of the week? In many countries, the week begins on Monday and not on a Sunday.

[igor-ribeiro]

Now, thinking about it, the property firstWeekday is the first day of the month in the week. We don't need to change that. What you want to change is the representation of the calendar property, because we assume it always starts on Sunday, which is false. I'll close the PR and I'll think about a solution for this. It's not that simple. I'm keeping the issue open.