sequencetools.Sequence is now registered with collections.Sequence.

This means that the following works:

    >>> sequence = sequencetools.Sequence(1, 2, 3)
    >>> isinstance(sequence, collections.Sequence)
    True

Why is this interesting?

`collections.Sequence` is the abstract base for `list`, `tuple` and our own
custom `TypedTuple` (and friends).

Because of this, statements like `isinstance(blah, collections.Sequence)` will
tend to allow more valid forms of input than our older `isinstance(blah, (list,
tuple)`.