Refactor code structure for improved readability and maintainability

samples/simple.lua

@@ -0,0 +1,21 @@
+effect = nil
+
+function _create()
+    local fxSrc = [[in vec2 vPosition;
+
+        void main() {
+            vec2 uv = vPosition * 0.5 + 0.5;
+            FragColor = vec4(uv, 0.5 + 0.5 * sin(uTime), 1.0);
+        }
+    ]]
+    effect = Effect.new(fxSrc)
+end
+
+function _update(dt)
+
+end
+
+function _render()
+    gl.Clear(0, 0, 0, 1.0)
+    effect:Render()
+end