Add OptionParameter

Closes #78

orx-gui/src/demo/kotlin/DemoOptions01.kt

@@ -0,0 +1,35 @@
+import org.openrndr.application
+import org.openrndr.color.ColorRGBa
+import org.openrndr.extra.gui.GUI
+import org.openrndr.extra.parameters.*
+import org.openrndr.math.Vector2
+
+/**
+ * A simple demonstration of a GUI for drawing a single circle
+ */
+
+enum class SomeOptions {
+    Default,
+    DoNothing,
+    Smile
+}
+
+fun main() = application {
+    program {
+        val gui = GUI()
+        val settings = @Description("Settings") object {
+            @OptionParameter("action")
+            var option = SomeOptions.Default
+        }
+
+        gui.add(settings)
+        extend(gui)
+        extend {
+            when(settings.option) {
+                SomeOptions.Default -> drawer.background(ColorRGBa.PINK)
+                SomeOptions.DoNothing -> drawer.background(ColorRGBa.BLACK)
+                SomeOptions.Smile -> drawer.background(ColorRGBa.YELLOW)
+            }
+        }
+    }
+}