Createcoverage

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- Added ``-t/--test-args`` command line option. The string passed to
that is passed straight on to the test runner. For instance, use
``-t "-m somemodule"`` to effectively run ``bin/test -m
somemodule``. Note the need for quotes (single or double) as you're
using an option to pass options... Fix by Godefroid Chapelle,
thanks!

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- Fixed a problem with opening the coverage ``index.html`` file on OS X when
using Python 2.7 or newer by using a file URL instead of a path.

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- Making the path to the coverage index.html file absolute before opening it
in the webbrowser. This prevents OSX from complaining that it isn't a URL.

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- Added option ("-d") for specifying an output directory. Specifying it also
makes sure the results aren't opened in a webbrowser (as the option is
intended for offline operation for automatic documentation generation
purposes).

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- Falling back to global 'coverage' binary if there isn't one in
``bin/coverage``.

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- Added missing MANIFEST.in file so that the distribution on pypi is complete
now.