Initial VTF support

[REDxEYE]

This pull request adds initial support for VTF image format

Changes proposed in this pull request:

• Add support for Valve Texture Format images

[REDxEYE]

Can I provide arguments to save the function? Like compression mode, flags and etc?

[radarhere]

Like im.save("out.vtf", compression=...)? Yes. Those arguments will become part of the im.encoderinfo dictionary.

[REDxEYE]

Yes, that's just what I needed, thanks!

[REDxEYE]

@radarhere Do I need to encode the image row-by-row or i can go like 4 rows at once because Bcn works in blocks of 4 by 4 pixels?
I never worked with Pillow C API, so i need some help

[radarhere]

@radarhere Do I need to encode the image row-by-row or i can go like 4 rows at once because Bcn works in blocks of 4 by 4 pixels? I never worked with Pillow C API, so i need some help

No, you don't have to.

A while ago, I attempted to implement DXT1 encoding. You might find that helpful - radarhere@363fab4

[REDxEYE]

I see, your attempt is quite close to what I wrote, but I used a different way to get 2 main colors for the block. Can I reuse some of your code from 363fab4?

[radarhere]

Feel free

[REDxEYE]

@radarhere Can you please review my bcn encoder?

[radarhere]

Slightly confused - this PR is still a draft, but you'd like a review?

Also, your lint problems could be resolved by just using the black formatting - REDxEYE#2. Is there a particular part of the styling that you dislike?

[REDxEYE]

Slightly confused - this PR is still a draft, but you'd like a review?

Also, your lint problems could be resolved by just using the black formatting - REDxEYE#2. Is there a particular part of the styling that you dislike?

I'm asking for a encoder code review, pr itself not even close to be ready :)