[orx-composition] reverse argument order in draw()

Add demos with comments

orx-composition/src/jvmDemo/kotlin/DemoCompositionDrawer02.kt

@@ -4,9 +4,18 @@ import org.openrndr.extra.composition.ClipMode
 import org.openrndr.extra.composition.composition
 import org.openrndr.extra.composition.drawComposition
 
+/**
+ * Demonstrates how to draw a Composition and how to use
+ * `ClipMode.REVERSE_DIFFERENCE` to clip shapes.
+ *
+ * The first shape clips part of the second one away,
+ * producing a shape that seems to be behind the first one.
+ *
+ * Without clipping, the second circle would cover part of the first one.
+ */
 fun main() = application {
     program {
-        val cd = drawComposition {
+        val composition = drawComposition {
             fill = null
             circle(width / 2.0, height / 2.0, 100.0)
 
@@ -15,10 +24,9 @@ fun main() = application {
             circle(width / 2.0 + 50.0, height / 2.0, 100.0)
         }
 
-
         extend {
             drawer.clear(ColorRGBa.PINK)
-            drawer.composition(cd)
+            drawer.composition(composition)
         }
     }
 }