v2.1.0

• Add d3.bin.
• Add d3.count. Thanks, @Fil!
• Add d3.minIndex.
• Add d3.maxIndex.
• Add d3.least.
• Add d3.leastIndex.
• Deprecate d3.scan; use d3.leastIndex instead.
• Deprecate d3.histogram; use d3.bin instead.
• Fix d3.permute to accept an iterable.
• Fix internal ES imports.