- search for ffmpeg libs/headers at cmake time
- added ffmpeg-transcode.cpp into libcommon if ffmpeg on
- hooked ffmpeg trancoding in common read_wav(...)
- passed test:
./main -m ggml-base.en.bin -f samples/jfk.mp3
* examples : refactor common code into a library
* examples : refactor common SDL code into a library
* make : update Makefile to use common libs
* common : fix MSVC M_PI ..
* addon.node : link common lib