Implement Engine, World, and system initialization

Signed-off-by: Daniel Henry <iamdanhenry@gmail.com>

include/Craft/World.h

@@ -0,0 +1,16 @@
+#pragma once
+
+namespace craft {
+class World {
+public:
+  World();
+  virtual void Begin();
+  virtual void Tick(float deltaTime);
+  virtual void FixedTick();
+
+  inline bool HasBegun() const { return mHasBegun; }
+
+private:
+  bool mHasBegun;
+};
+} // namespace craft