This method can be used for computing the bounding box of arbitrary GeoJSON
objects. This commit also fixes a bug in d3.geo.path, such that it will accept
any GeoJSON object, rather than requiring GeoJSON feature objects.
The renaming of attributes is totally not worth the hassle of maintaining an
externs file (or using the awkward `foo["bar"]` syntax). The file size
reduction from the advanced optimizations was negligible, besides!
This computes the projected area (in square pixels) of the given GeoJSON
object. This is useful for producing choropleth maps that area normalized to
the visible area.
Michael Bostock