Bridge POIs and Generated Maps

[zztong]

It would be nice if generated maps would/could place bridges over rivers instead of raising the terrain to make a land bridge. It would also be cool if we could make bridge POIs for the generator to select for placement. Off hand, the complications I see all have to do with making sure the POI is an appropriate size and the generator being able to detect where to align the POI with the roads it is generating. There are probably other issues too.