Django-wkhtmltopdf

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* Test sys.stderr to ensure it hasn't been overridden.

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* Fixed tests.
* Added option for not forcing download of PDF content. By default the content
is saved to a file, but can be displayed in the browser directly when
`show_content_in_browser` is set to True on `PDFTemplateView`.
* Removed duplicates when replacing STATIC/MEDIA paths.
* Fixed an issue when WKHTMLTOPDF_CMD consists of many parts.
* Fixed the local file paths so it works on Windows.

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* Removed override_settings code for rewriting the STATIC and MEDIA URLs as it
was not suitable for production use. It has been replaced with a string
replace for just now, but a proper HTML parser may be required in the future.

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* Fixed a bug with unicode characters.

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* Refactor of the PDFTemplateView to expose more options as class attributes.
* Addition/restructuring of several settings: `WKHTMLTOPDF_CMD`,
`WKHTMLTOPDF_CMD_OPTIONS`, `WKHTMLTOPDF_DEBUG`, `WKHTMLTOPDF_ENV`.
* Reliable methods of passing command line arguments to the binary.
* Add compatibility by default with `staticfiles` and `django-compressor`.

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* Fix a bug where temporary files were removed before the PDF was generated
when using the header & footer options.
* Only set the `Content-Disposition` header in the response if `filename` is set.
* Added a Makefile for deployments.
* Added 2.6 requirement to the README.