mainkai

Definition of zoom level does not follow conventions

2

Hi, first of all, thanks for the great library. I noticed that the implementation of zoom levels uses a strange and unclear [definition](https://github.com/msteiger/jxmapviewer2/blob/c6fefa78eb68fe8e7d5bc318863d740a9b007afa/jxmapviewer2/src/main/java/org/jxmapviewer/JXMapViewer.java#L67), leading to 0 being the maximum possible...