AW: container for different types, avoiding boiler plate

[Markus.Schnell@infineon.com]

> As you can see, functions ggender and gnumber are so trivial that
> hardly need to be declared at all. You can just use fetch
> directly. There is no need for Maybe. In fact, if you attempt to fetch
> a type that you didn't put into the attrs, you get a _compile-time_
> error.

Before I use your code, I have to understand it - this may take a
while... :)
But I'm not sure if it's suitable for what I'm doing, as the attributes
get inserted at run time, and not all of them appear everywhere. So
Maybe is quite natural here.

Markus