* Support ES6 arrow function (issue 517)
* Support ES6 Unicode code point escape (issue 521)
* Improve the speed and accuracy of comment attachment (issue 522)
* Support ES6 default parameter (issue 519)
* Support ES6 regular expression flags (issue 557)
* Fix scanning of implicit octal literals (issue 565)
* Fix the handling of automatic semicolon insertion (issue 574)
* Support ES6 method definition (issue 620)
* Support ES6 octal integer literal (issue 621)
* Support ES6 binary integer literal (issue 622)
* Support ES6 object literal property value shorthand (issue 624)