Move to pyproject.toml approach

[jwallwork23]

Closes #15.
Closes #13.

The best practice for Python packaging these days is to use a pyproject.toml file rather than setup.py and requirements.txt files. This PR sets that up.

The PR also sets up automatic linting and formatting and applies it across the codebase. (The vast majority of the changes are formatting changes.)

To review this, it is sufficient to check:

• pyproject.toml
• .github/workflows/test_warpmesh.yml

[jwallwork23]

Also dropped some "old" configuration files and "backup" versions of scripts. They are all under version control so multiple versions are unnecessary.

[jwallwork23]

@erizmr Please could you review that you are happy with the following?

• the pyproject.toml file.
• the updated test suite test_warpmesh.yml.
• Dropping configs/configs_old.
• Dropping warpmesh/generator/swirl_solver_backup.py and warpmesh/generator/swirl_solver_backupbackup.py.

The rest of the changes are just formatting and linting changes.

[jwallwork23]

I tried to put both @erizmr and @chunyang-w down as reviewers but it appears that you can only request one reviewer on a private repo.

[erizmr]

LGTM! Thanks!

[jwallwork23]

Thanks @erizmr!