Generalize IndexRange.

[sergetsyba]

Create an interface Range<T> extends Sequence<T>, which guarantees monotonicity of its items. Change IndexRange to IntRange and implement Range<Integer>.

Problems:

• Range<T> has no additional behaviour over Sequence<T>;
• adds unnecessary complications to IndexRange with no benefit, other than generalisation;
• implementing IntRange.get(Range<Integer>) -> Range<Integer>
  • may have different results depending on whether Range<Integer> is monotonically increasing or decreasing;

[sergetsyba]

IndexRange now conforms to Sequence<Integer>.