Pip Auto Reshim Support

[matan129]

Solves #37. Inspired by the npm version.

[johnklehm]

@danhper @pierreneter

[humitos]

Hi! I came here after reading multiple issues on asdf, the pre/post hooks implemented and the revert of them because of the problem reported with exec.

I'd like to see this feature merged into the asdf-python plugin since it seems that does not modify the core of asdf and only wraps the pip command in a basic way to reshim if it was called with install or uninstall --which sounds to exactly what the user will do manually anyway. Actually, this is what pyenv has been doing as well https://github.com/pyenv/pyenv/blob/master/pyenv.d/exec/pip-rehash/pip#L26

I was wondering if we want to apply the same logic for conda and easy_install as they do (see https://github.com/pyenv/pyenv/tree/master/pyenv.d/exec/pip-rehash). Maybe for other package managers like pipenv, poetry and pdm as well? (I'm not sure about these ones, but worth asking about them 😄 )

[matan129]

@danhper thoughts?

[danhper]

Hey, sorry for the delay!
This looks great, thanks a lot!