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Updated dependencies to support Python 3.5 and 3.6. These versions
do not yet pass formal validation, but they do seem to work in
informal testing. This is the start of a push to fully support
these most recent Python implementations, and to improve support
for interactive code (REPL or Jupyter Notebook).

Tweaks and testing for new version of underlying ``options``
module that returns operation to Python 2.6.

Major documentation reorg.

Code cleanups and additional testing. Test coverage now 77%.

Added ability to give ``show.inout`` decorator its own
parameters. Deprecated ``show.retval``, which is now redunant
with ``show.inout(only=''out'')``.

Test coverage bumped to 71%.

Added ``show.where()`` as a marker for "where am I now?" Improved
docs, esp. for ``where``, ``inout``, and ``retval`` methods.
Improved testing. Now at 67% line coverage.