Latexpages

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Added ``--only <part>`` command-line option for single article compiling.

Bypass ``multiprocessing.Pool`` when single-process rendering is requested.

Workaround multiprocessing issues with ``KeyBoardInterrupt``.

Improved ``__main__.py`` invocation support on Windows.
Document workaround for launcher installation issues.

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Fixed broken manual install due to ``setuptools`` automatic ``zip_safe``
analysis not working as expected.

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Added wheel.

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Added cleaning command for deleting intermediate and output files.

Allow to set default number of processes and engine in config file.

Added support for ``python -m latexpages`` invocation.

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More informative exception on failed texify/latexmk/pdftk execution.

Improved example to leave out the empty page at the end.

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Documentation fixes.

Improved example.