Multipolygon relations report their geometry as 'area' and are rendered
as such. However, they do not render a stroke. The stroke rendering
will come from the individual lines, which are given the tag
classes of their parent relations, allowing them to have a stroke
style matching the style of simple areas with the same tags.
Untagged circular ways are no longer considered areas. This prevents
an untagged inner way of a multipolygon from rendering as an area and
is consistent with how P2 and JOSM treat them.
In the CSS, it's no longer necessary to deal with multipolygons
explicitly in selectors. But keep in mind that area boundaries can
now be rendered either as lines or as area strokes. In most cases
the selector should be `path.stroke.tag-_____`, i.e. an explicit
`.area` or `.line` classes should not be included.
Finally, the parent ways of selected multipolygons are given the 'selected'
class.
This doesn't address stacking multipolygons, or interleaving
areas and multipolygons. More and more, I'm thinking we should
just merge the two into a unified "area" geometry.
An entity that is a member of a relation will have the classes
`member`, `member-role-<member role>`, and `member-type-<relation type>`.
The first use of these classes is to avoid filling multipolygon
member areas.
Now that Graph#parentWays is cached, the specialized Graph#parentStructure
method is no longer necessary.
This commit also demonstrates that it's relatively easy to write specs for
rendering now!
