If you provide a bad wkhtmltopdf option, you should get an exception

If you provide an invalid wkhtmltopdf option and wkhtmltopdf fails to
execute, you should be told about this straight away, by an exception
being raised.
Make tests work with python3
Merge pull request #8 from rory/master

If you provide a bad wkhtmltopdf option, you should get an exception
Merge remote-tracking branch 'jazzcore/master' into master_jazzcore
fixed old tests and created new tests to multiple css files