docs: improve badges

[realguse]

What is the purpose of this pull request?

• Documentation update

Description

Switches the style of the badges in the readme to flat-square or for-the-badge to get a more modern look, updates the alt tags for the badges, the badges now use same "color declaration" (small-case, hex code, excluding %23 which is not necessary etc.)

This is also one of the cleanest readmes I've seen in a long time, so that made it really easy to edit.

Before Submitting

• I've read the Contribution Guidelines.
• I've checked if there was an existing PR that solves the same issue.

[realguse]

Closing because I'll move it to a bigger pr that generally improves the whole readme (not to drastic changes though)