Drop-down select list.
It's the usual select box which opens a drop-down list when clicked on, similar
<select> html tag.
Under the hood, a select list is a special type of menu with a single entry having a submenu.
val create :
?action:(int -> unit) ->
?fg:Draw.color -> string array -> int -> Layout.t
create string_array i creates a select box with preselected entry
i. For instance
create [| "A"; "B"; "C" |] 1 will create a select box
with default choice
action (if specified) is executed when an
item is selected, and takes as argument the index of the selected item.