PR 408's cmakelists.txt file has too many issues (OpenCL breaks on Windows/OSX) and changing our options to have the "BASISU_" prefix will break upstream builds.
- Optimized ETC1S encoder (3-4.5x faster)
- Added optional SSE 4.1 support to encoder
- Switched from std::vector to a custom vector in the encoder and transcoder
- Added CppSPMD (SSE only for now)
- UASTC RDO is now more effective, but the command line parameter controlling qualiy has changed (to "lambda")