generate missing builders

[bilelmoussaoui]

Generates the following builders:

• Gtk.AdjustmentBuilder
• Gtk.CellRendererBuilder
• Gtk.IconViewBuilder
• Gtk.ShortcutLabelBuilder
• Gtk.ShortcutsWindowBuilder

There are still some builders to be generated, but I think they don't make sense

• Gtk.WidgetBuilder base class
• Gtk.ArrowBuilder deprecated
• Gtk.MiscBuilder base class
• Gtk.ContainerBuilder base class
• Gtk.BuilderBuilder I'm not sure about this one?
• Gtk.CellAreaBuilder base class
• Gtk.CellAreaContextBuilder base class
• Gtk.EventControllerBuilder base class
• Gtk.IMContextBuilder no idea
• Gtk.NativeDialogBuilder I don't think anyone creates a NativeDialog other than a Gtk.NativeFileChooser
• Gtk.GestureBuilder base class
• Gtk.GestureSingleBuilder base class
• Gtk.MenuShellBuilder base class
• Gtk.SettingsBuilder I'm not sure about this one, most of the time you use the default settings, but it could be useful if you're writing lower level stuff with Rust & GTK
• Gtk.RangeBuilder base class
• Gtk.TreeModelFilterBuilder no idea
• Gtk.TreeModelSortBuilder no idea
• Gtk.TreeSelectionBuilder no idea

[EPashkin]

@bilelmoussaoui Please fix order https://travis-ci.org/github/gtk-rs/gtk/jobs/698999324#L970

[EPashkin]

@bilelmoussaoui Thanks. 👍

[GuillaumeGomez]

Travis CI won't pass because of examples. Fixed them in https://github.com/gtk-rs/lgpl-docs/pull/74.

Thanks @bilelmoussaoui !