#4 watermark scaling enhancements

[Kaloyan K. Tsvetkov]

Recently I've been thinking about how to improve the watermark scaling. Right now the scale factor is applied to the watermark image without any regard to the image being watermarked. Let me show you an example: you have an image that is 100x100, and you have a watermark that is 800x800; since the watermark is bigger, the watermark scaling will try to reduce it by the defautl scaling factor, which 0.25 (1/4), so the watermark will become 200x200 and it will be still bigger than the image that's about to be watermarked. The solution
is to tie the scaling factor not to the dimensions of the watermark, but to the dimensions of thre image, so when the scaling factor is 1/4, this means that the watermark will become 1/4 from the size of the watermarked image. Using 100% (1.0) as scaling factor will cover the whole image w/ the watermark. Anyway, I don't want to drop the way the scaling is applied right now, so probably there will be a new "mode" for the scaling, and the available options will be: ASIDO_WATERMARK_SCALABLE_DISABLED, ASIDO_WATERMARK_SCALABLE_ENABLED_TARGET (current implementation) and ASIDO_WATERMARK_SCALABLE_ENABLED_SOURCE (the feature I just explained)