Added split/join methods to Sawyer::Container::Interval
Added IntervalSet::invert
Removed two-argument interval constructor

This avoids confusion about whether b is the interval size,
the last item, or one past the last item in the Interval(a,b)
constructor.

If b is the size, use Interval::baseSize(a, b)

If b is the last item, use Interval::hull(a, b)

If b is one past the end use Interval::baseSize(a, b-a) or
Interval::hull(a, b-1).
Added progress bar suffix object
Fixed compile error for Interval::isWhole
Documentation