[orx-shapes] Add alpha shapes (#203)

orx-shapes/src/demo/kotlin/DemoHobbyCurve02.kt

@@ -0,0 +1,26 @@
+import org.openrndr.application
+import org.openrndr.color.ColorRGBa
+import org.openrndr.extra.shapes.AlphaShape
+import org.openrndr.extra.shapes.hobbyCurve
+import org.openrndr.math.Vector2
+import kotlin.random.Random
+
+fun main() = application {
+    program {
+        val points = List(20) {
+            Vector2(
+                Random.nextDouble(width*0.25, width*0.75),
+                Random.nextDouble(height*0.25, height*0.75)
+            )
+        }
+        val alphaShape = AlphaShape(points)
+        val c = alphaShape.create()
+        val hobby = hobbyCurve(c.segments.map { it.start }, closed=true)
+        extend {
+            drawer.fill = ColorRGBa.PINK
+            drawer.contour(hobby)
+            drawer.fill = ColorRGBa.WHITE
+            drawer.circles(points, 4.0)
+        }
+    }
+}