add an example of a single-file project

my current starting point for prototyping new ideas with OF looks like this:

#include "ofAppGlutWindow.h"
#include "ofMain.h"

class ofApp : public ofBaseApp {
public:
    void setup() {
    }
    void update() {
    }
    void draw() {
    }
};

int main() {
    ofAppGlutWindow window;
    ofSetupOpenGL(&window, 1280, 720, OF_WINDOW);
    ofRunApp(new ofApp());
}

that's a single-file project contained entirely in a main.cpp. i like it because it means i don't have to answer questions like "should this go in the header or not" when i'm only prototyping a small idea.

@bilderbuchi just suggested that it might be helpful to have a minimal example like this in the examples folder to show people how they might construct a single-file example for reporting bugs or suggesting features (for example like https://github.com/openframeworks/openFrameworks/issues/1674#issuecomment-11756116). i think that could be really cool, and i'd be glad to add this if other people are also interested. so this issue is more to gauge interest.

p.s.: as an aside, it would be cool if we had a macro like this:

#define ofStart(appName, width, height, windowMode) \
int main() {\
    ofAppGlutWindow window;\
    ofSetupOpenGL(&window, width, height, windowMode);\
    ofRunApp(new appName());\
}

and ofMain.h included ofAppGlutWindow.h, then a minimal single-file example would look like:

#include "ofMain.h"
class ofApp : public ofBaseApp {
public:
    void setup() {}
    void update() {}
    void draw() {}
};
ofStart(ofApp, 1280, 720, OF_WINDOW);

this idea is from cinder, which uses:

#if defined( CINDER_MAC )
    #define CINDER_APP_BASIC( APP, RENDERER )                               \
    int main( int argc, char * const argv[] ) {                             \
        cinder::app::AppBasic::prepareLaunch();                             \
        cinder::app::AppBasic *app = new APP;                               \
        cinder::app::Renderer *ren = new RENDERER;                          \
        cinder::app::AppBasic::executeLaunch( app, ren, #APP, argc, argv ); \
        cinder::app::AppBasic::cleanupLaunch();                             \
        return 0;                                                           \
    }
...

Start by reviewing the existing examples folder and the proposed single-file main.cpp shown in the issue. Add a minimal example that demonstrates this structure, and consider only the requested example scope; completion means the example is present and usable for prototyping or reproducing issues.