Release 0.15.1

What's Changed

• AVX StackBlur column pass by @awxkee in #16
• Improvements on NEON stack blur by @awxkee in #17
• Fast gaussian, speed by 30% by @awxkee in #18
• Fast gaussian next, improvements by @awxkee in #19
• Box blur +10% by @awxkee in #20

Full Changelog: 0.15.0...0.15.1