def pie_slice(center, options)
      vertices = arc_vertices(center, options)
      vertices.unshift(:point => center)
      if options[:stroke_both_sides]
        closed_curve(vertices)
      else
        open_curve(vertices)
      end
    end
def pie_slice(center, options)
      vertices = arc_vertices(center, options)
      vertices.unshift(:point => center)
      if options[:stroke_both_sides]
        closed_curve(vertices)
      else
        open_curve(vertices)
      end
    end
options must include :radius, :start_angle, and :end_angle
 startAngle and endAngle are in degrees
 if an optional :stroke_both_sides option is true, then both
 sides of the slice will be included for stroking. the default is
 to just stroke one side since this will tend to be used to build
 up an entire circle, and if both sides were stroked, then we
 would get double-stroked lines where two pie slices shared a
 (not usually noticeable, but would be if transparency were used)

 0 degrees is directly right and 90 degrees is straight up
 arc will be drawn counterclockwise from startAngle to endAngle