forward and backward coloring for custom overlay

[tiptoptom]

Use case
Coloring the left and right side of a street instead of it's center when the key contains :forward or :backward
E.g. for a custom maxspeed overlay

Why
Coloring custom overlay based on tags is nice, but creates too many colors when forward and backward is included in the keys.

Proposed Solution
When coloring key matches a key containing :forward or :backward, colors the left, right or both side(s) of the street instead (like the bicycle or sidewalk quest)

For my understanding, the solution should be almost identical to #403

[tiptoptom]

Unfortunately it is not that easy because it depends on whether there is left or right traffic.

[Helium314]

Simply coloring the sides like done for left/right should be relatively simple. Actually coloring left/right half of the road is considerably more effort as there is nothing like that in SC.

Unfortunately it is not that easy because it depends on whether there is left or right traffic.

That's not a problem, SC already has some functionality to check for that.