Add support for direction=* in stop positions

[swaree]

Hi,

I have encountered a bus route that uses the same two-way road two times, one in each direction, stopping at different stops along the way. I have added stop_positions to these platforms with direction=backward or direction=forward.

Relatify seems to not recognize this indication and lists platforms as if they didn't have a stop position. I think it will be useful to include this feature as it influences routing and reduces the margin for error.

Many thanks for this tool, cheers.

[osm-spiregrain]

Here's another pathological example: Relation 16808482.

I believe it's currently mapped correctly via JOSM. It has one 'double back' section into St Austell station, and one bonkers double-back-then loop-around (so that it passes the same ways three times, and the same stops twice) centred around Bojea (node 11407787285 twice, and node 682277539 once.

Most of these Cornish routes around St Austell have a least one double-back.