KtxBundle is basically an in-memory representation of a KTX file.
Our primary motivation for introducing this class is to have a
structured container for block-compressed textures.
Note that this class is defined in libimage rather than libimageio.
There are several reasons for this:
1. The texel data in a KtxBundle is not meant to be decoded by the CPU.
2. It has no dependendencies on any libraries (stb_image tinyexr etc).
3. We wish to use it with WebGL, which needs to avoid using imageio.
e4b60e47cb
