Unresolved references using Ubuntu 16.04

[Miha-x64]

Hello. Thanks for your work, looks promising! Using Ubuntu 16.04, I can't compile it because of 'Unresolved reference's. E. g. in Widget.kt

...
import libgtk3.gtk_widget_get_focus_on_click
...
import libgtk3.gtk_widget_queue_allocate
...
import libgtk3.gtk_widget_set_focus_on_click

are red. Looks like there's no such deps in GTK+ version currently installed in my system.

[kropp]

I only tested it on Ubuntu 18.04 with GTK 3.22 I will release the generator later, so it will be possible to generate bindings for any GTK version