Take into account clipping when computing areas.

This can be optimised later.
Take into account clipping when computing centroids.
Respect clipping for line and point centroids.
Optimise d3.geo.path.area.
Optimise d3.geo.path.centroid.
Simplify.
Clarify convex polygon comment.
Fix loss of significance for d3.geom.polygon.area.
Set node velocity to zero when fixed.

This should avoid unintended jitter on mouseover.
Merge branch 'geo-area' of https://github.com/jasondavies/d3 into 3.0
Merge branch 'drag-android' of https://github.com/jasondavies/d3 into 3.0
Add placeholder d3.geo.centroid.
Add d3.shuffle. Fixes #948.
s/º/°/g
Merge pull request #949 from jasondavies/°

s/º/°/g
Add d3.geo.centroid.

Polygons are temporarily treated as lines while I work on adding area
weighting.

See #941.
Simplify.
Add d3.geo.area.

See #941.
d3.geo.area: return positive areas.
d3.geo.area: improve handling of tiny polygons.