Pycookiecheat

- Add firefox support , thanks to grandchild
- Also would like to welcome grandchild as a new member of the
pycookiecheat team!

- Add support for Brave thanks to chrisgavin!
- Add support for Slack thanks to hraftery!
- Migrate config to pyproject.toml alone
- Minor cleanup to codebase and tests

- No noteworthy API changes, hence the bugfix version bump, but some major
infrastructure and testing updates:
- Now uses GitHub Actions instead of Travis
- Now uses Playwright for testing, to actually open a Chromium instance and
use a real `Cookies` database
- PEP517
- black
- Now requires python >= 3.7
- This is largely due to requiremets of Playwright:
https://pypi.org/project/playwright/, which is only a *test* dependency
- Because I can't *test* with <=3.6, I'm not listing it as compatible,
though it *probably* will still work
- Migrate to pyproject.toml

- Try to open Chrome database in read-only mode to avoid db locked errors (29)

- db6ac6d Go back to using cryptography due to
https://www.cvedetails.com/cve/CVE-2013-7459/
- c70ad51 Allow users to override password (thanks alairock)

- Optionally outputs cookies to a file compatible with cURL (thanks to
Muntashir Al-Islam!)