v0.3.0

This release addresses performance concerns relating to extraneous object and closure creation.

• Uses a single d3.local instead of two.
• Eliminate use of function.bind.
• Fewer new closure creations on component render.
• Eliminate new D3 selection creation on component render (select(this) memoized in local).
• One fewer new object on setState (at the cost of losing immutability of the internal state object).