Idea: Prefer unpaived but not longer than % of time

[ullivilli]

Prefer unpaved is awesome.
Prefer small roads would be a good combination.

But some times you have e.g 5h for to do a 2h (motorway) drive.
So it would be cool to have a function to take small roads and unpaved roads but still make the destination in a reasonable timeframe.
Some times it calculates the 2h with unpaved roads to 20h and that makes it rather unusable.

I.e prefer unpaved and small roads and allow the route to take e.g 20%/50% etc longer than the fast route.