Creating IntervalTrees & inserting intervals

New intervals can be added to an IntervalTree with the push! function.

xs = IntervalTree{Int, Interval{Int}}()
push!(xs, Interval{Int}(500, 1000))

A more efficient means of building the data structure by bulk insertion. If the intervals are knows up front and provided in a sorted array, an IntervalTree can be built extremely efficiently.

intervals = Interval{Int}[]
# construct a large array of intervals...

sort!(intervals)
xs = IntervalTree{Int, Interval{Int}}(intervals)