Feature request: Add a function for getting the gu_init variable in libgu

[sharkwouter]

Right now it is not really possible to know if libgu has been initialized. This is a problem when you want to offer a library that can give warnings or connect to the internet, since those can only work if libgu has been initialized.

I can do this myself, but I don't want to forget to do it at some point. That is why I made this issue.