week number support

[Imre Horvath]

Dear Erlang/OTP Team!

I have started a project on GitHub because I needed the ISO Week Number for a given date and I wanted it in Erlang. Since the calendar module in the stdlib-1.17.1 application of Erlang/OTP R14B did not provide this functionality, I decided to write it myself. It's based on the calendar module and was tested successfully with eunit.

Though currently it's not in a fork of erlang/otp but in a separate repository https://github.com/imrehorvath/iso_8601_erl you might want to consider including it into OTP if you think it would be useful!

Best regards,
Imre