Bug in Tutorial / Documentation: Missing h-files

[notebook <notebook22312 gmail com>]

Hello Devs:

On this site:
https://developer.gnome.org/gtk3/stable/ch01s04.html

there are reference to h-files like exampleapp.h. But their content is never listed on the website. This 
renders the tutorial rather useless. It would be awesome, if someone could update the documentation regarding 
that point.


Regards
Chris