Find shortest intermodal route

Calculates an intermodal route between a source (lat, lon) and a target (lat, lon). A point can be any reasonable geo-position on the planet, even on land. Reasonable means that it must be somewhere in the ocean or nearby a waterway or street. However, a routing from or to the mountaintop of Himalaya is not supported. The underlying network covers the sea based on AIS-data as well as rivers, canals and even main roads from openstreetmap.org. But it does not contain OSM's minor street types like residential or service. A routing between cities of different continents usually returns a partial passage over the sea. In this case the crucial points, the via-ports, have an additional un/locode-attribute attached.