Review paganin

First raw review of the Paganin part I am not sure about it but I guess compute_filter and pad_with_values should also be protected ?

Some raw ideas that you might be interested in (maybe this is already the case):

• add CI on the project (I am sure you can find help on the team)
• include a module 'units' to define clearly what are the units used and maybe add some helpers for conversion. It might help if the project grows.
• include the bootstrap and run_test files from silx