2.8.0

• Add selection.datum (deprecating selection.map), which is like selection.data but doesn't compute a data-join; it can be used to get or set the data bound to elements.
• Brush component can now take decorative resizers.
• Add d3.map class (similar to ES6's map collection) for easier management of string-value maps; this is used internally by transitions, event listeners, the nest operator, and many other components.
• Add d3.bisector for bisecting sorted arrays with an accessor.
• Expose d3.selection.enter.prototype.
• Generalize d3.svg.mouse to support HTML elements, and renamed to d3.mouse.
• Add d3.scale.identity.
• Add axis.tickValues.
• Rewrite d3.behavior.zoom.
• Add "start" and "end" events to force layout, along with force.tick and force.alpha for synchronous execution.
• Add a variety of new time interval methods.