3.0.0

• Moved classes from inc/ to src/
• Removed static methods from WpStash
• Added singleton to WpStash
• Improved usage of Config
• Added sanitization to Config::$driverClassName
• Implemented env var support.
• Allowed to support base64 decoded strings as WP_STASH_DRIVER_ARGS because of..
  • security reasons
  • working with environment vars does not allow " in values, which invalidates JSON/serialized strings