Ordering from top-bottom or bottom-top about bmp-js

[SamJakob]

Yes this is a real edge case. Traditionally Microsoft bitmaps are stored bottom-to-top, however there is a convention of sorts that if you wish to store a top-to-bottom bitmap, you set the height to be negative true height.

In other words, positive height means bottom-to-top whereas negative height means top-to-bottom. In both cases, the height is the magnitude of the height value.

[dejavu1987]

I had the same issue, I created a pr to fix just that #41