Added ability to use virtual scroll with different sized of elements
flag "enableUnequalChildrenSizes" was added (defaults to false) to bypass the different-height elements calculations (for users with fixed-height children to avoid the minor performance impact).
Breaking Change: The value of ChangeEvent.end wasn't intuitive. This has been corrected. Both ChangeEvent.start and ChangeEvent.end are the 0-based array indexes of the items being rendered in the viewport. (Previously Change.End was the array index + 1)