The characters comprising a border. By default, borders are made of unicode
box-drawing characters, but they can be changed to arbitrary characters via
this struct.
A list of MenuEntrys, in the order they appear when rendered,
with a description of how the text of the selected and normal
(ie. not selected) entries should be rendered.
An instance of a menu, with a selected entry.
When a MenuInstance is rendered, the
currently-selected entry is rendered using
the Menu’s selected_info.