Merge pull request #5 from tianon/patch-1

added check to passed in options for definedness of each option
Merge pull request #6 from tianon/patch-2

updated to use Array.forEach instead of for (... in ...) to avoid issues with prototypes (and avoiding explicit hasOwnProperty)
fixed a few small inconsistencies/inefficiencies

These explicitly broke r2d3 support, presumably because Sizzle is less forgiving than the selectors in proper d3-supported browsers.
Merge branch 'r2d3' of github.com:tianon/radar-chart-d3

* 'r2d3' of github.com:tianon/radar-chart-d3:
  fixed a few small inconsistencies/inefficiencies