Towards lane support

[basicNew]

In this PR:

• Added basic lane support while keeping old functionality. You can now add lates to a road at a given offset and later ask to the lane for its geometry. All the waypoint calculation is still done in the roads and all the exporters that rely on that still see roads as single lane. However, the street plot generator only uses the road / lane geometry, so new features are visualized when using the --debug flag. The final next step (in a future PR) will be to move all the intersection computation so it ca be lane-based.
• Separated classes into their own files.
• Changed simple example so the ringroad is a single, two-lane trunk.

Examples:

Simple city builder with two-lane trunk ringroad. Only the road geometry was defined and the two lanes were derived.

As an example, here is the same city with a 4-lane ringroad

Finally, the PCG city:

[garyservin]

LGTM