Allow destructuring pattern in arrow functions passed as arguments or on LHS

It didn't work for arrow functions on the rhs or passed as argument. I.e. the following constructs threw a syntax error:

```
var x = ([a, b]) => 42;
foo(([a, b]) => 42);
```

Since arrow functions are usually used as argument for other functions, destructuring in arrow functions was useless so far.

Since I have only little experience with parsers, there may be a better way to do this....
Updated this to

    if (expr.type === Syntax.Identifier ||
        (starts_with_paren &&
          (expr.type === Syntax.ArrayExpression ||
          expr.type === Syntax.ObjectExpression))) {