Happy New Year 2017 🎉

• No longer support Node.js v4.x, use v6.0+
• Convert callback APIs to promises(StyleStats#parse())
• Drop test specs feature
• Drop Handlebars（no longer support custom/markdown/html formats）
• Add prettify flag and function #106
• Rewrite some code in ES6
• Update module dependencies
• Use ava test runner instead of mocha