For handling diffs abstractly. A range is a subarray of the two original
arrays with a constructor defining its relationship to the two original
arrays. A Same range contains a series of elements which can be found in
both arrays. A New range contains elements found only in the new array,
while an Old range contains elements found only in the old array.
A Replace contains two arrays: elements in the first array are elements
found only in the original, old array which have been replaced by elements
in the second array, which are elements found only in the new array.