- update to version 7.0:
* Drop support for Python 2.6 and 3.3.
* Wrap ``click.Choice``'s missing message.
* Add native ZSH autocompletion support.
* Document that ANSI color info isn't parsed from bytearrays in
Python 2.
* Document byte-stripping behavior of ``CliRunner``.
* Usage errors now hint at the ``--help`` option.
* Implement streaming pager.
* Extract bar formatting to its own method.
* Add ``DateTime`` type for converting input in given date time
formats.
* ``secho``'s first argument can now be ``None``, like in ``echo``.

* Fixes a ``ZeroDivisionError`` in ``ProgressBar.make_step``, when the
arg passed to the first call of ``ProgressBar.update`` is 0.

* Show progressbar only if total execution time is visible.
* Added the ability to hide commands and options from help.
* Document that options can be ``required=True``.
* Non-standalone calls to ``Context.exit`` return the exit code,
rather than calling ``sys.exit``.
* ``click.getchar()`` returns Unicode in Python 3 on Windows,
consistent with other platforms.
* Added ``FloatRange`` type.
* Added support for bash completion of ``type=click.Choice`` for
``Options`` and ``Arguments``.
* Only allow one positional arg for ``Argument`` parameter
declaration.
* Add ``case_sensitive=False`` as an option to Choice.