Transition from setup.py to pyproject.toml

[kozo2]

Created pyproject.toml branch
https://github.com/ecell/ecell4/tree/pyproject.toml

[kozo2]

It seems that poetry does not work with ecell4-base.

kozo2@DESKTOP-RCVTTB6:/tmp/ecell4$ poetry add ecell4-base
Using version ^2.0.4 for ecell4-base
Updating dependencies
Resolving dependencies... (0.1s)
Writing lock file
Package operations: 2 installs, 0 updates, 0 removals
  - Installing ecell4-base (2.0.4)
[EnvCommandError]
Command ['/home/kozo2/.cache/pypoetry/virtualenvs/ecell4-r7K9jc16-py3.6/bin/pip', 'install', '--no-deps', 'ecell4-base==2.0.4'] errored with the following return code 1, and output:
Collecting ecell4-base==2.0.4
  Cache entry deserialization failed, entry ignored
  Could not find a version that satisfies the requirement ecell4-base==2.0.4 (from versions: 1.0.dev1, 1.0.dev2, 1.0.0, 2.0.0b1)
No matching distribution found for ecell4-base==2.0.4