List of acceped files :
  * mxl : compressed musicXML score (linkef to ots txt expresseur-description)
  * xml : musicxml score
  * txt : a text file which describes the score parmeter, or a text file which conatains the list of chords for improvisation.
  * png : a one-page score to be displayed wuth the list of chords for improvisation.
  * txb : list of chord-graphic-rectangle in the png (built by Expesseur Graphic User Interface)
