Tiny Optimisations + Nice Castles

A couple things added recently:

• 🏰 Added new Castle and Graveyard assets from the Low Poly Medieval Castle Pack by Ventuar3D (on the Unity Asset Store)
• 🎥 Added ambient occlusion post-process, to make that castle look good
• 🧠 Replaced Unity's navmesh agents with a custom script to increase performance (still not perfect but will push gradual fixes and improvements in the future)
• 🚧 Updated Unity to the latest version