Debug utility

[levithomason]

This PR addresses the TODO in #206 to add a logging utility. It is only used in the Dropdown for now as the Dropdown is our proving grounds for removing jQuery and setting our v1.0.0 precedence.

Two debug logs were generating object differences, see componentWillReceiveProps and componentDidUpdate. This logic was pulled into an objectDiff util and tested.

[levithomason]

Logs are auto namespaced to stardust:<your-name>

[levithomason]

console methods group, groupCollapsed, and groupEnd are added for cleaner console activity.

[dvdzkwsk]

Couple of thoughts:

1. Even though the debugger will noop during production, the arguments are still always evaluated. This is needlessly expensive in production or even outside of debug mode, especially for more complex operations. Consider lazily running debug statements, i.e.:

debug(() => object.diff(...))

The above is a solution if the following is not an option

2. As a corollary, all of these debug statements are still invoked in production, their argument evaluation notwithstanding, even if they are just noop. I know it's a lot of work to wrap everything in environment checks, but for a public library I think it could be optimized a bit further. The pattern used here is similar to what we do in our business apps, but that's a bit of a different realm than a public library. Not sure if there's an easy way to abstract this logic so it's removed at compile time, but it should be considered.

[levithomason]

Agreed on all counts and considered these things prior to the PR. In the future we'll have an optimization phase which will include a transform to remove debugs, static propTypes, and static_meta from production code.

I want to get more components moved to the 1.0 pattern before optimizing further. This PR moves us from console statements to a debug pattern we can iterate on.