Range spec

Range:
Min/Max rather than Start/End, better naming when dealing with non-contiguous ranges.
Start and end values are inclusive.

How enumeration works for stepping, etc is left to the class to decide, provide a static class with some standard implementations that use Math<T>.

Assumption is the main IRange<T> can be either contiguous or non-contiguous
Assumptions for SubRanges():
    No two sub-ranges overlap.
    Each sub-range is atomic (ie contiguous).
    Sub-ranges are returned in order of their Min value.
    No sub-range is ever empty.

Min/Max throw an InvalidOperationException if IsEmpty == true.

interface IRange<T> : ISet<IRange<T>>, IEquatable<IRange<T>> {
  T Min { get; }
  T Max { get; }
  bool IsEmpty { get; }
  IEnumerable<IRange<T>> SubRanges();

  bool Contains(T value);
}