Refactor inventory unequip logic to use item ID instead of equip target; update README for inventory and skill tree progress

README.md

@@ -15,15 +15,15 @@
 
 ## Inventory system
 - [ ] Inventory UI
-- [ ] Inventory database
-- [ ] Inventory item database (items, consumables, equipment)
-- [ ] Inventory item interactions (use, equip, unequip, drop)
-- [ ] Inventory item stacking
+- [x] Inventory database
+- [x] Inventory item database (items, consumables, equipment)
+- [x] Inventory item interactions (use, equip, unequip, drop)
+- [/] Inventory item stacking
 - [ ] Inventory item sorting (UI)
 
 ## Skill tree system
 - [ ] Skill tree UI
-- [ ] Skill tree database
-- [ ] Skill tree interactions (learn, unlearn, upgrade)
-- [ ] Skill tree requirements (level, skill points, other skills)
-- [ ] Skill tree effects (TBD)
+- [x] Skill tree database
+- [/] Skill tree interactions (learn, unlearn, upgrade)
+- [/] Skill tree requirements (level, skill points, other skills)
+- [x] Skill tree effects (TBD)