Support BC5_SNORM and BC7

[pepperoni505]

I'd like to use this library, but it doesn't support certain DDS files, such as BC5_SNORM and any BC7 file. Is this something that will be supported in the future?

[drewcassidy]

BC7 might happen eventually, but BC7 is a completely different format that is far more complicated than BC1/BC3, with no commonality

as for BC5_SNORM, that's only "unsupported" due to most image formats (including how Pillow works internally) not supporting signed images. The data is identical though: You just have to remap between (0, 1) and (-1, 1)

[drewcassidy]

Do you need BC7 encoding or just decoding? I may tackle decoding after my next refactor

[pepperoni505]

If possible, encoding and decoding would be very useful