gtkdialog: hseparator widget reference

# hseparator widget A GtkHSeparator ## Definition
    <hseparator tag_attr="value"...>
    </hseparator>
“…” denotes acceptance of multiples of the same thing. ## Tag Attributes See the GtkHSeparator widget and ancestor class properties. The following custom tag attributes are available:
Name | Description | Value | Since
--- | --- | --- | ---
space-expand | Pack widget expanding into space | `true` or `false` |
space-fill | Pack widget filling space | `true` or `false` |
## Directives None. ## Notes This widget was introduced in version 0.7.21. button, checkbox, chooser, colorbutton, comboboxentry, comboboxtext, combobox, edit, entry, eventbox, expander, fontbutton, frame, hbox, hscale, hseparator, list, menubar, menuitemseparator, menuitem, menu, notebook, pixmap, progressbar, radiobutton, separator, spinbutton, statusbar, table, terminal, text, timer, togglebutton, tree, vbox, vscale, vseparator, window,