v3.0.0

• Massively improved performance. Index now takes ~2x less memory and generating tiles is overall 20% to 100% faster (with bigger gains on heavier datasets).
• Removed "clipped square" heuristics (they were complicating the codebase without a noticeable performance gain).
• Added a descriptive error when passing zoom higher than 24.
• Added TopoJSON support to the demo page.