Carto variant and sample project

[mojodna]

This introduces a second set of views (with the same names) intended for use with Carto. Specifically, it removes the outline, inline, and casing geometries provided for rendering and uses attachments instead.

This also ports the Cascadenik project and stylesheet to Carto for compatibility with TileMill. It's been restructured somewhat to be more concise, so it's no longer a 1:1 match (although it renders almost identically).

In addition, a high_road function is now created that takes the place of each of the views so that a project only needs a single layer added and it will choose an appropriate view using !scale_denominator!. See the sample project for usage.

[mojodna]

This also incorporates #9.