Implement ES2015 class feature (part II.) (#2439)

This patch is the second milestone of the implementation of this new language element.

Supported:
 - Single class inheritance
 - Functionality of 'super' keyword
 - Implicit constructor in class heritage
 - Specific behaviour while extending with the built-in 'Array' or '%TypedArray%' object
 - Abstract subclasses (Mix-ins)

JerryScript-DCO-1.0-Signed-off-by: Robert Fancsik frobert@inf.u-szeged.hu

jerry-core/parser/js/js-parser.h

@@ -83,6 +83,7 @@ typedef enum
   PARSER_ERR_MULTIPLE_CLASS_CONSTRUCTORS,             /**< multiple class constructor */
   PARSER_ERR_CLASS_CONSTRUCTOR_AS_ACCESSOR,           /**< class constructor cannot be an accessor */
   PARSER_ERR_CLASS_STATIC_PROTOTYPE,                  /**< static method name 'prototype' is not allowed */
+  PARSER_ERR_UNEXPECTED_SUPER_REFERENCE,              /**< unexpected super keyword */
 #endif /* !CONFIG_DISABLE_ES2015_CLASS */
 
   PARSER_ERR_LEFT_PAREN_EXPECTED,                     /**< left paren expected */