Simplified build-from source story. Build requirements no longer include setuptools itself. Project can no longer be installed from source on pip 19.x, but install from source is still supported on pip < 19 and pip >= 20 and install from wheel is still supported with pip >= 9.

Simplified build-from-source story by providing bootstrapping metadata in a separate egg-info directory. Build requirements no longer include setuptools itself. Sdist once again includes the pyproject.toml. Project can no longer be installed from source on pip 19.x, but install from source is still supported on pip < 19 and pip >= 20 and install from wheel is still supported with pip >= 9.

Expand on the change in the changelog.
Expand on the change in the changelog.
