Improve `CustomSource` in the example

The ultimate goal is to make it look more like a regular openFrameworks application.

example/src/CustomSource.cpp

@@ -1,6 +1,6 @@
 #include "CustomSource.h"
 
-CustomSource::CustomSource(){
+void CustomSource::setup(){
 	// Give our source a decent name
 	name = "Custom FBO Source";
 

example/src/CustomSource.h

@@ -5,14 +5,10 @@
 
 class CustomSource : public ofx::piMapper::FboSource {
 	public:
-		CustomSource();
-
-		// These are overrides of FboSource virtual functions.
-		// FBO sources are not executing before they have been assigned to a surface.
+        void setup();
 		void update();
-		void draw(); // You don't have to care about fbo.begin() or fbo.end() here
+		void draw();
 
-	private:
 		vector <ofRectangle> rects;
 		vector <float> rectSpeeds;
 };