Add option for pre-commit

[veit]

• pre-commit offers a framework for running hooks before committing code.
• Config pre-commit-config.yaml:

  repos:
    - repo: https://github.com/psf/black
      rev: 19.10b0
      hooks:
        - id: black
          language_version: python3.7
          # override until resolved: https://github.com/ambv/black/issues/402
      files: \.pyi?$
          types: []
  
    - repo: https://gitlab.com/pycqa/flake8
      rev: 3.7.9
      hooks:
        - id: flake8
          language_version: python3.7
  
    - repo: https://github.com/asottile/seed-isort-config
  rev: v1.9.4
      hooks:
        - id: seed-isort-config
  
    - repo: https://github.com/pre-commit/mirrors-isort
  rev: v4.3.21
      hooks:
        - id: isort
          additional_dependencies: [toml]
          language_version: python3.7
  
    - repo: https://github.com/pre-commit/pre-commit-hooks
      rev: v2.4.0
      hooks:
        - id: trailing-whitespace
        - id: end-of-file-fixer
        - id: debug-statements
  

• Run pre-commit run --all-files