def draw_simple_line(p1, p2, z_index, colour)
      draw_line(p1.x, p1.y, colour, p2.x, p2.y, colour, z_index)
    end
def draw_simple_line(p1, p2, z_index, colour)
      draw_line(p1.x, p1.y, colour, p2.x, p2.y, colour, z_index)
    end
Simplify drawing a line.

 There are dire warnings in the Gosu documentation for draw_line() which
 suggest that line drawing should only be done for debugging purposes.

 * +p1+        [Point] Beginning point
 * +p2+        [Point] Endpoint
 * +z_index+   [Fixnum] Z-order
 * +colour+    [Gosu::Color] Colour of line