1.5 (important bug fix and ES6 class syntax)

Thanks to @TMiguelT this release makes use of ES6 class syntax resulting in clearer and more concise syntax and easier extendability for users.

Also a critical bug was fixed that was not tested before and therefore slipped through for a long time: When using a context sensitive production that should match for both sides, eg: 'A<B>C:' 'X', only the left side was checked, instead of both. This would lead to incorrect results in situation that the left matches but the right side does not. It has been fixed and a new test case has been added to cover this situation.