(introduced in 0.7.0-DEV) more thoroughly. It is not compatible with 0.6.

In addition, it fixes a bug in container_loops.jl in which the length()
function when applied to subranges (i.e., inclusive(a,b,c) or
exclusive(a,b,c)) returned the length of the whole container instead
of the length of the subrange. (There should be no value returned
for the length of the subrange since the data structure does not support
an O(1) algorithm or even O(log n) algorithm to compute the length.)

Some other smaller changes in this commit are as follows.

    IntSet was changed to BitSet (name change in 0.7.0-DEV)
    Small updates to documentation
    Some assert statements in balanced_tree.jl that were present
    during development are deleted.