Poland population and farming model

[atiff]

Thanks guys.

I found a bug in one of the formulae; have fixed, and will post the updated file later (on another computer right now). Basically, it didn't recalculate the numbers properly if you changed the efficiency of the farming from '100'.

My next project is detailing Kepno County (south of Kalisz) using some of these numbers as a baseline. I want to do this for Krakow and environs in the longer run, but want to tackle something smaller first