Add and configure initial pre-commit hooks

[IndexSeek]

This PR adds a configuration for pre-commit and aims to implement standardizations to prevent future syntax errors, typos, bad formatting, and styling inconsistencies.

For now, the only hooks being used are:

• https://github.com/asottile/pyupgrade
• https://github.com/PyCQA/isort
• https://github.com/PyCQA/autoflake
• https://github.com/codespell-project/codespell

Some people may prefer black rather than [autoflake]; we could look to do this instead if preferred.

I added tox to the dev extras in setup.cfg.

Closes #168