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)
removed a bunch of unused things (especially options) and updated the maxValue logic

Now, we can pass in a maxValue option to actually get the graph to go to at least 5, for example, even if none of our data goes that high.