Reduce lexer's memory consumption

src/libjsparser/lexer.h

@@ -148,6 +148,7 @@ typedef struct
 token;
 
 void lexer_init(const char *);
+void lexer_free (void);
 void lexer_run_first_pass( void);
 token lexer_next_token (void);
 void lexer_save_token (token);