fully incorporated gadm2 data with gadm2->iso function and helpers

An admin map for gadm 2.0 is stored in `resources/gadm.zip`. At compile time, it is unpacked and converted to a dictionary, much as for the original gadm 1.0 dataset. The gadm2 id is given by the `objectid` field in the gadm2 shapefile, and can be used to retrieve ids for the different admin level polygons (levels 0 to 5).

```clojure
(gadm2-map 100000)
=> {:iso "KEN", :ids {:id5 3230, :id4 1028, :id3 234, :id2 43, :id1 7, :id0 118}}

(:iso (gadm2-map 100000))
=> "KEN"

(:id0 (:ids (gadm2-map 100000)))
=> 118
```