* consolidate common operations into functions
* test imports in test_preprocessors
* skip rather than fail on tests which require pandoc if we can't find it
* move svg2pdf inkscape-finding into a function which doesn't raise exceptions, allowing us to skip test if inkscape can't be found, and skip accordingly
* use urllib instead of requests in svg2pdf preprocessor
* fix flake8 complaints
* rename `jupyter_contrib_nbextensions.extensions` -> `jupyter_contrib_nbextensions.nbconvert_support`, since they're now all nbconvert things
* rename `tests/test-postprocessors.py`, since it actually tests preprocessors!
* move highlighter config scripts into `config_scripts` package
* remove redundant scripts in `src/jupyter_contrib_nbextensions/nbextensions/highlighter`
Josh Barnes