unzip a zipped file
[rep,stat,err]=sci_unzip(zipfile,dir_out)
* zipfile = the whole address of the zip file to unzip
* dir_out = the directory where to locate the unzipped files
* rep = a column vector of character strings (standard output)
* stat = an integer, the error status. stat = 0 if no error occurred
* err = a column vector of character strings (standard error)