getter for chart specification?

I'm using v0.9.2 and trying to implement this example using error bars (hacking it a bit to show lower and upper confidence intervals): http://cedar-v0.surge.sh/examples/errorbars.html

I have a rendered chart, though when I attempt to access the specification it doesn't seem to be available in the object. The specification object appears to be under a `chart._definition` object instead, `console.log(chart)`:


And when I attempt to access it via `chart._definition.specification` it turns up _undefined_.

Start with the linked error-bars example and inspect the rendered chart object in v0.9.2, especially chart._definition and chart._definition.specification. Trace how the chart specification is stored and determine the supported access path; done means the specification can be retrieved reliably from the chart object.

Written by the indexing model from the issue text.