v2.0.0

Major release, focused both on CI, setting contribution guidelines and following community standards. Some minor bugs were also fixed.

Some of the most important changes are the following ones:

• Fixing Menu::Item's constructor bug (initializer lists wouldn't work for C++ versions prior to C++17).
• Adding a CI system with GitHub Actions, including on-push and on-PR testing.
• Adding templates for PRs and Issues on GitHub.
• Updated CppSafeIO's used version.
• Created Code of Conduct, Contribution Guidelines and Security Policy.

Full Changelog: v1.0.0...v2.0.0