remove hard dependency on geos library.

The typical usage of parsing osm files does not require handling of multipolygons (and area() call is no used) . However, handler.hpp  includes area.hpp file which in turn includes geos library. And that one defines int64 types in global scope which conflicts with other libraries i am using.
Merge pull request #65 from romange/patch-1

Remove hard dependency on geos library.