Simplify main.cpp example + makefile cleanup.

[arturoc]

yes, i've been doing this to test the normal examples, probably we should change all the examples to have the main like this, i can do it with a script and send a pull request, we could have specific platform examples for rpi or other boards to show some special features but the rest should be the same as desktop i think

we can add a example for desktop showing how you can pass a custom window to add fsaa antialiasing for example, we changed the syntax of main to the current one some versions ago so people knew that the window can be used like that so we'll need to check with zach and thoe but i think as long as we have an example it's ok to go back to the default window syntax

[bakercp]

It would be great if all the examples got rid of the glut stuff. It would make testing much easier.

Your idea of a single custom windowing example to show off that feature is ideal.

Otherwise, let's let the oF internals figure out the right windows!