Added support for JavaScript switch statement.

[pawelpel]

Solution based on newly introduced OpenHard and CloseHard tokens. When closing tag couldn't be matched then we check if there is any OpenHard token in the stack. Then level is set to its predecessor.

Ref. #41

[JaapJoris]

I think I found an example that breaks it:

<!-- Switch inside function -->
<script>
    function foo() {
        switch (a) {
            case b:
                break;
        }
        }
        </script>