Arkansas "Marine Fuel Tax" shields

[claysmalley]

Certain numbered routes in the Arkansas State Highway System have a special "Marine Fuel Tax" design. These are currently tagged network=US:AR. A decision would need to be made on tagging of the network=* value, and whether this would add any special cases, before support can be added to this project.

Compared to the standard Arkansas state route shield, the Arkansas shield is color-swapped, the ref of the road is shrunk and moved to the bottom of the state outline, additional text is added along the top, and line art is placed in the middle. Marine Fuel Tax routes have "MARINE FUEL TAX" as their top text, a person fishing from a boat as the line art, and a white-on-brown color scheme.