Generate a chart from any type of data array

The .date function should be used like this:

``` js
var eventDropsChart = d3.chart.eventDrops()
.date(function(d){ return d.date; });

d3.select('#chart_placeholder')
.datum(data)
.call(eventDropsChart);`
```

Instead of

``` js
var eventDropsChart = d3.chart.eventDrops();

d3.select('#chart_placeholder')
.datum(data)
.date(function(d){
return d.date;
}),
.call(eventDropsChart);
```

Start at the eventDrops chart entry point and compare the two .date invocation examples in the issue. Reproduce both data-binding patterns in the chart, then verify that the accessor is applied correctly when .date is configured before or after the chart is called.

Written by the indexing model from the issue text.