Add features from the envy project

[sametmax]

Envy (https://github.com/shaunvxc/envy) is an interesting project letting you edit a module in your env, then revert it back to it's pristine state, without using versioning tools. It's useful for debugging installed libs, and it's a perfect fit for a pew subcommand. After all, who wants to install a 100 virtualenv managing tools ?

[berdario]

Yeah, it's nice... but I don't think I'll implement this any time soon. Is integrating it as a dependency of pew what you had in mind (similarly to what I did with Pythonz)?

[sametmax]

Nice idea.