Support for IntervalSets (discontinous intervals)

[kvesteri]

IntervalSet should support at least the following operations:

• union
• intersection
• length (sum of the lengths of all intervals in this set)
• radius (length / 2)
• degenerate
• empty / bool / nonzero
• discrete
• contains (True if given point / Interval / IntervalSet is contained within this IntervalSet)
• eq (True if the set represents the same interval as another value)
• ne
• open (True if all the intervals in the set are open)
• closed (True if all the intervals are closed)

[kvesteri]

Probably not in the scope of this package after all.