gtk3: suppress deprecation warning
gtk3: suppress unused warning
gtk3: remove trailing spaces
Merge pull request #205 from cosmo0920/suppress-warning-gtk

Suppress deprecation warning and Implement New GTK+3 API

Patch by cosmo. Thanks!!!
gtk3: use rb_ary_new() directly

Because the two values are not car/cdr relation. It means that thery
are not an element of an associative array. They are just two values.
gtk3: remove a needless space
gtk3: remove needless NULL checks
gtk3: Gtk::Container#focus_chain returns nil when focus chain is not set explicitly

It is a backward imcompatible change. Use the following code to ensure
getting an array:

    container.focus_chain || []
gtk3: remove unused variables
gtk3: use an unused variable
gtk3: unindent
gtk3: add a missing space
gtk3: use meaningful name
gtk3: use GVAL2RVAL_UNSET()
gtk3: use unused variable
gtk3: unindent
gtk3: add a missing space between ")" and "{"
gtk3: use GVAL2RVAL_UNSET()
gtk3: use meaningful name
gio2-gi: add experimental GObjectIntrospection based Ruby/GIO2 bindings