Lots of fixing and rearranging of code

previous code was not working, for several reasons:
1. I had swapped use_duration and frequency arguments in Person constructor. This happened because the Ruby code I looked at explicitly sets the variables, while Julia will automatically assume constructors take arguments in the same sequence as members are defined in the type.

2. I assumed find(fn, collection) would return an array of matching objects. But instead it returns an array of indices of the matching objects.

There are still problems. The data is not stored correctly in the CSV file. All numbers get stored in one column instead of multiple rows with multiple columns.