Replace DrawImage implementation for draw.Transformer.

[iopred]

This change has no API modifications and looks a little bit better.

[llgcode]

Hi @iopred, I think that original implementation treat rotation, using a transformation matrix. The scaler that you using doesn't take this transformation matrix in parameter. You need to take care of rotation/shear transformation if you want to be compatible with previous version of the function. Surely scaling and translation is 90% of usual case.
These implementation have better performance or results in common cases?
Thx @iopred

[iopred]

Of course! Sorry I was really tunnel visioned. I will make the modifications to support draw.Transformer.

I think the performance is similar, it's the result which is better, I'll get an example for you.

[iopred]

Ok, I have updated it to use Transformer instead.
Attached is two images, the avatars and the small emote are noticeably smoother.

Before:

After:

Open the images, it's very noticeable around the emoji image.