Since removal of local python modules and moving them to global
scope can leave *.pyc files behind and cause confusion, I think that it's
reasonable to disable local imports by using from __future__ import absolute_import.
Because code is written without this bad practice of importing local packages,
there is no need to change how we import things, so only change is adding
futureimport at the beginning of each file.
I have searched and found out that there is no way how to disable it globally
(see https://stackoverflow.com/questions/13773861/how-can-we-make-future-imports-global),
so I have added it to each file in libtaskotron/ and libtaskotron/directives.