first-day-of-week doesn't work as expected

[DavidGriffith]

I thought that the first-day-of-week parameter would make the leftmost column that day of the week. For instance, if first-dat-of-week is 6 for Sunday, the order remains the same with Monday on the left concluding with Sunday or the right. Only the color of the day of the week and the date is changed.

Correction: It looks like if I use 6 to indicate that the day of the week starts on a Sunday, the days are positioned correctly, but the day of the week abbreviations remain as Monday through Sunday.

[DavidGriffith]

After further analysis, it seems clear that the current behavior is unintended because if the third parameter is used and is something other than zero, the result is an incorrect calendar. I've prepared a pull request to fix this in #6.