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

orx-shapes/src/demo/kotlin/DemoHobbyCurve01.kt

@@ -0,0 +1,17 @@
+import org.openrndr.application
+import org.openrndr.color.ColorRGBa
+import org.openrndr.extra.shapes.hobbyCurve
+import org.openrndr.math.Vector2
+
+fun main() = application {
+    program {
+        extend {
+            val points = listOf(Vector2(150.0, 350.0), Vector2(325.0, 100.0), Vector2(500.0, 350.0), Vector2(325.0, 250.0))
+            drawer.stroke = ColorRGBa.BLACK
+            drawer.fill = ColorRGBa.PINK
+            drawer.contour(hobbyCurve(points, closed=true))
+            drawer.fill = ColorRGBa.WHITE
+            drawer.circles(points, 4.0)
+        }
+    }
+}