jsonpickle: add support for Python 3.4

collections.OrderedDict has a different __reduce__()
representation on Python 3.4.

Add a custom handler to paper over differences in in the reduced
representation.  The OrderedDictReduceHandler produces a
compatible flattened output so that the on-disk representation
is consistent across python versions.

Closes #68

Reported-by: @Arfrever via github.com
Signed-off-by: David Aguilar <davvid@gmail.com>