refactor: move styles to a resources package

[andreoliwa]

Proposed changes

• Move styles to a nitpick.resources package
• Pave the way to rely more on resources and less on fetching styles from GitHub
• Nitpick might even be able to run on https://pre-commit.ci/, because no external HTTP requests will be done
  • running Nitpick on pre-commit.ci doesn't work; there is nothing installed on a local hook
  • maybe with a proper Git hook, Nitpick will be able to validate itself on pre-commit.ci? 🤔
  • for now, I will keep using GitHub Actions, running Nitpick on tox

+ which python
/venv/bin/python
+ python -m nitpick fix
Traceback (most recent call last):
  File "/usr/lib/python3.8/runpy.py", line 185, in _run_module_as_main
    mod_name, mod_spec, code = _get_module_details(mod_name, _Error)
  File "/usr/lib/python3.8/runpy.py", line 144, in _get_module_details
    return _get_module_details(pkg_main_name, error)
  File "/usr/lib/python3.8/runpy.py", line 111, in _get_module_details
    __import__(pkg_name)
  File "/code/src/nitpick/__init__.py", line 2, in <module>
    from loguru import logger
ModuleNotFoundError: No module named 'loguru'

Checklist

• Read the contribution guidelines
• Run make locally before pushing commits
• Add tests for the relevant parts:
  • API
  • CLI
  • flake8 plugin (normal mode)
  • flake8 plugin (offline mode)
• Write documentation when there's a new API or functionality

[coveralls]

Pull Request Test Coverage Report for Build 1635909014

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.08%) to 96.324%

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Totals
Change from base Build 1635642165:	0.08%
Covered Lines:	1944
Relevant Lines:	1994

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💛 - Coveralls

[github-actions]

🎉 This PR is included in version 0.30.0 🎉

The release is available on:

• v0.30.0
• GitHub release

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