tickit_pen_new() creates a new TickitPen instance. It initially has no attributes set.
tickit_pen_new_attrs() creates a new TickitPen instance and populates it with a given list of attribute
values. The attributes are given as pairs; first a TickitPenAttr then an integer giving its value,
terminated by a final 0 or -1.
Two additional attribute types are recognised here, TICKIT_PEN_FG_DESC and TICKIT_PEN_BG_DESC. These will
expect to receive a string argument value, which will be parsed as for
tickit_pen_set_colour_attr_desc(3).
tickit_pen_clone() creates a new TickitPen instance. It initially has the same attributes values set as
the one given by orig.
The reference count of a newly-constructed pen instance will be one. This can be incremented or
decremented using tickit_pen_ref(3) and tickit_pen_unref(3). When its reference count reaches zero it is
destroyed.