v0.3.0 (v4.0.0 upstream)

Updated to v4.0.0-51-g4eca0ef3 upstream:

• Arm's reference ASTC encoder is now built in-tree
  • Added Rust wrappers for the newly-added KTX2 ASTC compression support.
• KTX-Software is now built with CMake by cargo
  • This requires CMake, Python and other utilities on the build machine.
  • No need for a wholly-separate Rust build system anymore - this should make future maintenance easier.
• Linux builds now always link to libstdc++; BSDs (& macOS, iOS, Android) link to libc++
  • This fixes all linking errors regarding exception handling personality (__gxx_personality_v0).
  • Windows builds are unaffected by this change.