added changes needed for running script on OSX

This is the modified script for downloading all data files into macintosh. The following changes were needed:
1- Set encoding to LATIN-9
2- OSX uses a different 7-zip application
3- OSX needs you to specify a path to perl when using read.xls
4- OSX needs you to specify a path to unzip application
5- I had to add some folders to the paths leading to the extracted files
6- OS is case sensitive: cur file stem needs and extension need to be in the right case