Expose stable Python API

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• I have searched the documentation and believe that my question is not covered.

Feature Request

Howdy folks,

Our build system is mostly written in Python, so it'd be nice if I could consume poetry's CLI from Python.

As an example, I'd love to be able to do things like:

import poetry.poetry

project = poetry.poetry.Poetry("./my/path")
project.lock()  # Mirrors 'poetry lock'
project.add(...)  # I think you get the idea

(This would also be helpful for my test suites operating on fake projects, as I can generate them on-the-fly).