A very simple perl module that models a calendar month.

This function returns a data structure representing the dates in a month. The
data structure returned is an array of array references. The first level array
represents the weeks in the month. The second level array contains the actual
days. By default, each week starts on a Sunday and the value in the array is
the date of that day. Any days at the beginning of the first week or the end of
the last week that are from the previous or next month have the value undef.