Rename package and improve packaging standard

[mscheltienne]

Close #11

@deivit24 Seeing your positive feedback for the requested (backward incompatible) change, I took the time to open this PR with the proposed change. Feel free to commit on top of it; or to open a separate PR and close this one; if you prefer to fix the issue differently.

In this PR:

• The package name python-steam-api is maintained. pip install python-steam-api will still be the correct installation.
• The package directory is renamed from steam to steam_web_api, preventing naming conflicts with the larger https://github.com/ValvePython/steam The package can now be imported with:

import steam_web_api

from steam_web_api import ...

• The packaging format is upgraded from the legacy setup.py to the current standard, pyproject.toml
• The now unused files, MANIFEST.in, requirements.txt are removed
• The version number is added to the package in steam_web_api.__version__
• Set the minimum python version to 3.9 (matching many major package, matching the python SPEC (although they don't really apply on a non scientific package)

---

As a new user of this package, I would also like to make sure it adheres to the current coding standards to ensure it has a long and prosperous life. If you want, I can open a succession of short PR to:

• Add a workflow to release the package on PyPI -> A simple GitHub release will trigger the build and release on PyPI.
• Add linters and fix style -> I see that you used flake8, nowadays, ruff is the preferred linter and formatter. Personaly, I would add ruff, isort, codespell
• Add pre-commit configuration and pre-commit.ci for automatic style checks

Hopefully, the changes here will also be beneficial to other project you work on!

[mscheltienne]

Also, if you want the follow-up PRs, I would not release until I add those (would be very quick). And in any case, if you release with a new directory name (thus a new import), I would release a new major version, 2.0.0 to indicate the backward incompatibility.

[deivit24]

@mscheltienne Thanks again. any follow-up PRs will be nice if needed. I will play around with this over the weekend. I also some that you updated this to use toml! Thanks for that