decimal retired; roads and landcover read as one map

Eight styles now. decimal, the green single-hue style, read as the same map as blueprint and is gone; its names keep resolving. Two fixes land on every style: trunk highways draw at the highway's width so Highway 2 no longer breaks into pieces at mid zoom, and the low-zoom landcover hands over to the mid-zoom tint without going bare between z6 and z7.

• flavor=decimal, decimal-light and decimal-dark alias onto blueprint; theme code u03 decodes to blueprint and u04 is still blueprint
• roads_trunk joins every style between the major roads and the highway, in the flavor's link tone at the highway's width
• The stock landcover fill holds to z6 and eases to the landcover field's opacity at z7 instead of fading to nothing

Availabilityflavor=decimal, decimal-light, and decimal-dark still resolve. They alias to blueprint.