ASFML v3.0.0: update to the new major CSFML version

What's Changed

• New release 3.0.0 based on CSFML 3.0.0 by @mgrojo in #29

This is an API breaking release, although the changes to your application are straightforward.

See CSFML and SFML releases for more information:

• https://github.com/SFML/SFML/releases/tag/3.0.0
• https://github.com/SFML/CSFML/releases/tag/3.0.0

Changelog: https://github.com/mgrojo/ASFML/blob/master/CHANGELOG.md#sfml-300
Full Changelog: v2.6.1...v3.0.0