Add support for maxaxleload

[eisams]

OSRM routes through this road segment that has a max axle load of 0.8 tonnes, which I don't think would fit any normal car today?

https://wiki.openstreetmap.org/wiki/Key%3Amaxaxleload

Maybe the default should be 3.5t divided by two, as that's the limit of regular cars in the EU at least?