World map IV

This example tries to improve the previous one by introducing a way to show more labels as the zoom level increases. The "algorithm" is a poor man's level of detail computation that uses empirically found magic numbers with an inverse square root law. It probably would not work reasonably in other cases.

Also, a minor bug is solved: Apparently, vector-effect: non-scaling-stroke does not work with <use>, so the world's outline was not scale independent. This is solved by creating two different paths without relying on <use>.