Add checking min, max zoom levels.

Signed-off-by: Maksim Melnikau <maxposedon@gmail.com>
add download caching

Signed-off-by: Maksim Melnikau <maxposedon@gmail.com>
add project and organization information
use standard path for cache

Signed-off-by: Maksim Melnikau <maxposedon@gmail.com>