Added date_get_day_func, date_get_ordinal_suffix_func.

Changed date_from_ordinal_func and date_to_ordinal_func to use and
return a 1-indexed month. Changed get_month_string and
get_short_month_string to use this.
date_from_ordinal_func now handles day being higher than 365 on non-leap
year, and higher than 366 on leap year.