Roadmap to release `0.5.0`

[heinezen]

Release 0.5.0 should be the milestone that uses a stable version of the new engine architecture. This means that all legacy code paths are removed and only the new engine components are used at runtime. Basically, these components are:

• Renderer/Presenter (#850, #1492)
  • OpenGL
  • Vulkan (done later)
• Input system (#1501)
• Event System (#1008)
• Gamestate (#1377, #1515)
  • Game Entity
  • Components
  • Systems
  • Activities
• Modpack Converter (#1151)
  • Converter fixes
• Playtest demo (maybe using https://archive.org/details/AgeOfEmpiresIiTheConquerorsDemo)
• Documentation

Legacy code will probably remain in the release and then removed in later releases one by one.