Support pipenv as package manager

[Serkan-devel]

pipenv is a package manager, which makes dependency tracking and updating easier for each individual project.

[jberends]

indeed -- agreed. We need to move away from reqs.txt and into pipenv to create a better-world :tm:

[PsiACE]

That's a good idea. We'll add pipenv in the future, and we'll also consider poetry.

[apehex]

well change is coming your way :steam_locomotive:

I just made a PR which should give pipenv support out of the box.

hopefully I didn't blow this and it's at least a first step :D

now:

• "make init" creates a pipenv and installs the deps in it
• all the other rules are executed inside this env (test, tox etc)

[Zethson]

@moodule would you be interested in adding your fixes to the cookietemple cli-python template?

https://github.com/cookiejar/cookietemple/

The cli-python template originates from this template here and could certainly use your fixes.