[ADD] Github Actions workflows

[luisrgpt]

Since we are merging code to master using pull requests, and since we publish our code through releases, I've created the following workflows:

• push_commit.yml - When pushing a commit to GitHub, test the downloader and evaluate code quality;
• create_pull_request.yml - When creating a pull request, publish a package of the downloader into the testing environment of PyPI, to evaluate how the package will eventually be presented on the real PyPI;
• publish_release.yml - When publishing a release, publish a package of the downloader into PyPI.

For the workflows to work, some init.py were added, as well as a requirements.txt, and a setup.py with all metadata necessary for the package such as:

• project URLs: source code, issue tracker, homepage and funding;
• module location;
• classifiers, for the Pypi search engine;
• description, by using the content of the readme.md. The requirements.txt only serves as proxy for the "pip install -r requirements.txt" to use setup.py.

Also, the package name and all constants were renamed.

GitHub issues: #8 and #10

[FMCalisto]

This pull request was reviewed and addressed. Near concerns are now solved.