Some extra features (cairo, ConnectAfter(), GtkSettings, etc)

I have promised you, to send you new features from visionect/gotk3.
Please review the code. Constructive critics are welcome ;)

Best
Miha 
I ran into this problem in other places as well. It looks like many type-wrapper functions are package-private. I like making them public in case someone else wants to create their own bindings for a C library that depends on libcairo.