JoRobo: How to professionally manage extension development

So you created your own Joomla extension, maybe for a client, maybe for general usage, and now you're wondering how to best manage it for the future. You will have to handle bugfixes, store it somehow, create releases and maybe improve it with new features. So how could we do this? There are several ways you can do this, but today I'd like to show you the one possible solution that works good for me.