libopus library version 1.3.1.
The following changes have been made:
- Obviously, unnecessary folders and files have been removed.
- win32/version.h got added.
- config.h has been fixed to support Clang/LLVM for Windows.
- OpenMPT modifications are marked with "// OpenMPT".
- celt/x86/vq_sse2.c has been modified to check for OPUS_X86_MAY_HAVE_SSE2.
- silk/x86/*sse4_1.c has been modified to check for OPUS_X86_MAY_HAVE_SSE4_1.
- For building, premake is used to generate Visual Studio project files.
  See ../build/premake/ for details.