Added option to calculate height and/or width on render.

[matthull]

By default, uses height and width of anchor DOM element.
Can optionally specify function to use for calculation.

Doesn't address all the auto-sizing features listed in issue #295, but I'm finding it very useful for these scenarios:

• Have chart fill parent div, thus controlling chart size via CSS
• Have chart dynamically resize in response to user interactions (e.g. user changes top N count with slider)

[gordonwoodhull]

I don't know if Nick and Jacob would find this too clever, but I'd suggest allowing the width and height methods to take either a function or a value, in the d3 / crossfilter style.

[matthull]

I was leaning that way at first, but wasn't sure if it would be too much magic. Definitely keeps the API cleaner though - I felt a little dirty adding 4 new API methods just for this feature.

Thoughts, Nick/Jacob? Would something like the following be copasetic?
.height(50) // no change in behavior
.height(function(element) {...}) // set height calculation
.height("auto") // enables default height calculation - element.getBoundingRect().height or similar

[jrideout]

@matthull I like the approach you and @gordonwoodhull are thinking about. I implemented a version in #329. Let me know if you think that works. I didn't put in an "auto" option, but rather will "revert to default" on any falsy value to achieve the same thing. I find that a bit cleaner, but that's just my personal preference.

@gordonwoodhull Anything we can do to keep API style similar to crossfilter and d3 is a must. Our abstraction is purposefully very leaky, so we need environmental, not internal consistency to maintain the principle of least surprise. Plus d3.functor is cool.

[matthull]

I like it. To me the semantics of falsy triggering default are a little weird, but I think it's cleaner and easier to remember vs. using magic word like "auto."