Provide hook to get changed props along with the internal chart object

[jotak]

This would allow consumers to interact with the internal chart, call C3 API methods when something changed such as show/hide bools, legend, formats, etc. (anything but chart data)

[jotak]

Hi,
An example of usage I've in my code:

From my React component that uses C3Charts

  onPropsChanged = (oldProps, newProps, chart) => {
    if (this.state.showLegend && !oldProps.legend.show) {
      chart.legend.show();
    } else if (!this.state.showLegend && oldProps.legend.show) {
      chart.legend.hide();
    }
  };

In render:

        <C3Chart
          // ...
          data={this.seriesData}
          legend={{ show: this.state.showLegend }}
          onPropsChanged={this.onPropsChanged}
        />

[jotak]

I think it could address issues such as #33 and #38 ?

[bcbcarl]

@jotak: Looks good to me. Thanks!