Add an Italian Codice Fiscale module

This module validates 16 digit Italian tax codes for individuals.
https://en.wikipedia.org/wiki/Italian_fiscal_code_card

It is based on the pycodicefiscale module that can be found here:
https://github.com/baxeico/pycodicefiscale

Functions have been renamed to follow the stdnum naming scheme:
isvalid() -> is_valid(), control_code -> calc_check_digit(),
get_birthday() -> get_birth_date(), get_sex() -> get_gender(). The
build() function for generating tax codes (based on name, birth place
and date) has been left out because this number cannot be uniquely
constructed with this information alone (numbers are issued by the
Italian tax office with a mechanism handle duplicates).

Addresses trac ticket #9.