v6.0.0

• Changed: es5 -> es6
• Added: multiple options for postcss-url as array
• Added: multiple basePath as array
• Added: copy accept basePath param
• Changed: hash function to xxhash
• Changed: arguments in custom url callback
• Changed: no processing callback in inline without maxSize
• Changed: filter matches by asset path, relative to project (process.cwd)
• Changed: copy can work without postcss to option, but required assetPath