Extras: OpenStreetMap -- make some plan

[zverok]

What should/can be done here: evaluate OSM API and propose some reasonable API. It should go into Coord data type.

Some examples, which may or may not look reasonable:

city('Kharkiv').distance_to(city('Kyiv'))
city('Kharkiv').path_to(city('Kyiv'), transport: :auto)

# more complicated task:
Geo::Coord(..., ...).country 
# => should try its best to return inctance of Reality::Country
# same for City

# future super-features like:
city('Kharkiv').path_to(city('Kyiv'), transport: :auto).cities 
# => array of Reality::City the path goes throuhg

# what more?..

[zverok]

Considering accidental popularity of https://github.com/zverok/worldize, I'd say now there should be "bounding polygon" extracted from OpenStreetMaps also (and, this time, it seems another kind of extra -- CountryOSM, CityOSM and so on). We'll do pretty demo pictures as soon as possible.

[zverok]

(Though, I'm not sure those polygons are of good quality at OSM... Needs check.)

[zverok]

https://help.openstreetmap.org/questions/13615/extract-all-country-borders :-\

[zverok]

→ #62