Changes:
* replace `iotuil` elements with the ones from `os` package;
* replace `os.Filemode` with `fs.FileMode`;
* use `signal.NotifyContext` instead of `NewGracefulContext` (removed).
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Define database of Earth's polygons in GeoJSON format. Implement resolving
of geo point to continent in which it is located through point-in-polygon
calculation.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
