Adding a function to convert GHCN-Daily data

Hi, Remy - your code for converting GHCN data to CSV has been incredibly useful for a graduate school project I'm part of. I took your code and modified it to work with the GHCN-Daily (http://www1.ncdc.noaa.gov/pub/data/ghcn/daily/) data we've been working with, and wanted to contribute this back to your project. Cheers!