Use pipenv

[sephii]

And remove code that loads variables from envdir and use python-decouple to handle environment-specific settings: https://pypi.org/project/python-decouple/. This should also fix #23.

[simonbru]

Should we also use python-decouple to load variables in the fabfile ?

By the way, I tried activating the virtualenv from .bashrc by sourcing the activate script and it seems to work: simonbru/drifter@67e6e4b. Environments variables are not loaded when activating the virtualenv this way, but this may not be an issue if we load them ourselves with python-decouple.

Do you remember which issues you encountered when trying a similar approach ?

EDIT: Using python-decouple in fabfile is probably overkill