fastline   - draws a line to the graph buffer (fast!)
       - Input  (h,l) = (x1,y1)
       -        (d,e) = (x2,y2)
       -        a = line style
       -            0 = white
       -            1 = black
       -            2 = xor
       -            3 = pattern (one byte pattern stored in (mlinebitmap))
       - Output line draw to graphbuffer