Andy's very mini virtualenvwrapper-ish zsh plugin

This is a super-lightweight sort-of-clone of virtualenvwrapper; it pretty much expects you to be using pyenv (though you don't have to), and because it's based on the venv module, (creation) only works for python >= 3.3.

Anyway, see the comments in venv-lite.zsh for all you need to know.

Andy Gimblett, andy@barefootcode.com, 2017