Every map is a globe by default

Every unmap map now draws as a globe by default: a sphere zoomed out, flattening into Mercator as you zoom in. The flat map is still available by passing mercator as the projection.

• Every unmap map is a globe by default now, so there is nothing to pass to turn it on.
• Zoomed out the map is a sphere; zoomed in it flattens into Mercator.
• The flat map is still available: pass mercator as the projection instead.