Add Span interfaces to handle checks for overlaps, containment, equality, etc.

This is a contribution of a span class as discussed on the mailing list.

The classes are int and long based and can:

1. determine if points are within the span.
2. determine if one span contains another span
3. determine if two spans overlap
4. do not have to have 0 (zero) as the index origin.
5. determine the length of the span
6. determine the last position in the span.
7. determine the first position in the span.

Changes to Number Utils required to detect underflow and overflow calculations.