PR to make dfk Pip-installable and make publishing to PyPi easy

[Athiriyya]

This PR puts all code into a dfk_lib package, which can be pip-installed with all dependencies with pip install dfk_lib. Pushing updates to PyPi is simple with poetry build; poetry publish. The downside is that imports become longer than they were: (import hero.utils.utils as hero_utils becomesimport dfk_lib.hero.utils.utils as hero_utils) Otherwise, no code changes.

To test the PyPi publish mechanism, I did publish a package on PyPi. I'm happy to hand over the keys to that one, or take it down if you'd like, but for the moment it's there and will install this project and the web3 dependency from pip. LMK if there's anything you'd like changed.

• All code moved into a dfk_lib package so everything can be published together
• All examples updated with dfk_lib imports so they work correctly
• Added pyproject.toml file for dependency managment with Poetry. See: https://python-poetry.org/ for more info; basically, it's as close as Python comes to npm

[Athiriyya]

This was substantially resolved with 9fe666418bdfc1ae35f5873a021ffd40dab99945, so this PR is obsolete. Glad to see it all pip-installable as dfktools now!