20120822
========

I finally started to work on the "regions problem" 
in :mod:`lino.modlib.countries`.

`countries.City` is now designed to contain 
all geographic areas that are smaller than a 
Country (in the meaning of a sovereign state) 
and bigger than a Street.

The new choicelist CityTypes is an attempt to make a universal 
classification of the words that designate such areas.
A perfect classification is probably not possible, 
and it will possibly still evolve.

There are "country drivers" to limit the list of possible CityTypes for a given Country.

Partner.region is no longer a simple text field but also a ForeignKey.

The choices for Partner.region are Cities with a type < 50
The choices for Partner.city are Cities with a type >= 50.