Decoder for DXTn-compressed data

This crate provides methods to decompress DXTn-compressed image data. The decompression code was based on the original C code used in the Python Pillow Imaging package.

The following formats are currently supported:

• Bc1: 565 color, 1-bit alpha (dxt1)
• Bc2: 565 color, 4-bit alpha (dxt3)
• Bc3: 565 color, 2-endpoint 8-bit interpolated alpha (dxt5)
• Bc4: 1-channel 8-bit via 1 BC3 alpha block
• Bc5: 2-channel 8-bit via 2 BC3 alpha blocks
• Bc6: 3-channel 16-bit float

The following formats are not implemented:

• Bc7: 4-channel 8-bit

Format documentation: http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt

License: MIT, copyright Istvan Fehervari, Robert Nix