Fix for degenerate polygons.

TopoJSON arcs always have at least two coordinates. If a polygon is constructed
from a single arc, and that arc only has two coordinates, then the resulting
reconstructed polygon previously only had a single coordinate. According to the
GeoJSON specification, this is invalid: "A LinearRing is closed LineString with
4 or more positions. The first and last positions are equivalent (they represent
equivalent points)." And so, now when degenerate polygons are constructed, the
first point is duplicated to the end to satisfy the specification.
Combine tests.
Improve area accuracy for small polygons.

The use of cosines can introduce large rounding errors for small
distances.

Fixes #28.
Merge branch 'small-area' of https://github.com/jasondavies/topojson
Bump version.
Add new --simplify-proportion option.

This allows the proportion of retained points to be specified for
simplification, which may be friendlier than specifying an exact area.

This also includes a fix for NaN areas that were occurring due to small
negative values in the triangle area calculation (being passed to sqrt).
Error checking for --simplify-proportion.
Allow comma-separated --properties. Fixes #30.
Use defaults when missing from options.

Fixes #16 #17.
Merge branch 'simplify-proportion'
Update README.md
No, really, fix the wiki link.
Fix --simplify-proportion argument.
Allow multiple --id-property.
Bump version.
Make Node version dependency explicit.
Use console.log instead of fs.appendFileSync.
Shapefile parsing!

Also, you can now specify the object name for an input file by specifying an
input file of the form "name=path". For example:

  topojson -o us.json -- states=../us-atlas/shp/statep010.shp

Note that the -- is required here to avoid confusing with the bash shell.
Update topojson.version and src/package.js.
Use x for patch versions.