v0.3 - interface, namespace, fixes

What's Changed

• Read project version from file by @heinezen in #94
• Update documentation for C++20 by @heinezen in #96
• Update nyan_specification.md by @apainintheneck in #97
• Update meta_info.cpp by @trodge in #99
• Remove deprecated std::iterator class by @heinezen in #100
• Fix missing include for g++-13 by @heinezen in #102
• Fix a bunch of parser and interface errors by @heinezen in #103
• openage gamestate fixes by @heinezen in #106

New Contributors

• @apainintheneck made their first contribution in #97
• @trodge made their first contribution in #99

Full Changelog: v0.2...v0.3