New option to store descriptor files --output-dir
New option to store descriptor files --output-dir

Stores descriptor files in the output folder maintaining a nested
directory structure as in the input audio folder.

Both --output-dir and --output-json can be used simultaneosly

Do not use absolute path for audio filename keys.

MTG/essentia,carthach/essentia,MTG/essentia,carthach/essentia,carthach/essentia,MTG/essentia,MTG/essentia,MTG/essentia,carthach/essentia,carthach/essentia