Move to using a pyproject.toml and src layout

[forrestfwilliams]

To test:

python -m pip install cookiecutter
cookiecutter https://github.com/ASFHyP3/hyp3-cookiecutter.git -c src_and_pyprojecttoml

{fill out form}

cd {hyp3 plugin name}

git init .
git add .
git commit -m "Minimal HyP3 plugin created with the hyp3 plugin cookiecutter"
git tag -a v0.0.0 -m "Marking zeroth release for auto-versioning and CI/CD Tooling"

python -m pip install .

Package should install successfully and behave like a normal python package.

[forrestfwilliams]

Creating a repository with a name that does not include hyp3 lead to an error. Once a template repository is created, the issue can be re-created using:

import tomli
with open('pyproject.toml') as f:
    out = tomli.loads(f.read())