Dependencies with #head
At the moment, I cannot build Aporia with nimble, I get an error about version conflicts of the GTK wrapper.  However, if I hack the `aporia.nimble` file and remove `#head` from the GTK2 dependency then it will build fine. So I'm wondering if the practice of using  `#head` in a dependency is more likely to break?  Would it be a more reliable build if dependencies always used a version number? Just a thought...