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Changed name of parameter ``sep`` in ``hr``, ``title``, and
``sep`` methods because discovered it was conflating and
interfering with the ``sep`` parameter in the main options. The
horizontal separator character that is repeated N times is now
addressed as ``char``.

Added ``first_rest`` prefix helper. First line gets one prefix,
(all) subsequent lines get another. Prefix helpers reorganized
into their own submodule, ``show.prefixes``.

Fixed problem with Unicode stream handling under Python 2. It has
slipped under the testing radar, given too many mocks and not
enough full-out integration testing. Oops!

Updates testing for early 2017 Python versions. Successfully
packaged for, and tested against, all late-model versions of
Python: 2.6, 2.7, 3.3, 3.4, 3.5, and 3.6, as well as PyPy 5.6.0
(based on 2.7.12) and PyPy3 5.5.0 (based on 3.3.5). Python 3.2
removed from official support; no longer a current version of
Python and not well-supported by testing matrix.

Tested with Python 3.5.0 final.

Added ability to set styles for some methods such as ``title``,
``hr``, and ``sep`` as an overlay to class, object, and per-call
settings. This is a first delivery on what will become a general
feature over the next few releases. Added vertical spacing to
``title`` and ``sep`` methods for nicer layouts.

Increased testing line coverage to 96%, improving several
routines' robustness in the process.