For longer cases, factor out the logic to new functions.
For very short cases, just move the declaration before the switch.
v2: in one case, replace the switch with if/else.
Arrow signs are specific to submenu items, so they would be more natural
to be handled in menu.c rather than accepting "arrow" in
font_buffer_create().
Also I allowed non-positive numbers for max_width in font_buffer_create(),
in which case the natural font width is used as the buffer width.
<resize><drawContents>[yes|no] configures whether to let the clients
redraw its window content content while resizing.
When <resize><drawContents> is set to no, a multi-rect is shown to
indicate the geometry of the resized window.
