[orx-shapes] Add demos, tweak comments

orx-shapes/src/jvmDemo/kotlin/alphashape/DemoAlphaShape01.kt

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+package alphashape
+
+import org.openrndr.application
+import org.openrndr.color.ColorRGBa
+import org.openrndr.extra.shapes.alphashape.AlphaShape
+import org.openrndr.math.Vector2
+import kotlin.random.Random
+
+/**
+ * Demonstrates the use of [AlphaShape] to create a [org.openrndr.shape.ShapeContour] out
+ * of a collection of random [Vector2] points. Unlike the convex hull, an Alpha shape can be concave.
+ *
+ * More details in [WikiPedia](https://en.wikipedia.org/wiki/Alpha_shape)
+ */
+fun main() = application {
+    program {
+        val points = List(40) {
+            Vector2(
+                Random.nextDouble(width * 0.25, width * 0.75),
+                Random.nextDouble(height * 0.25, height * 0.75)
+            )
+        }
+        val alphaShape = AlphaShape(points)
+        val c = alphaShape.createContour()
+        extend {
+            drawer.fill = ColorRGBa.PINK
+            drawer.contour(c)
+            drawer.fill = ColorRGBa.WHITE
+            drawer.circles(points, 4.0)
+        }
+    }
+}