doc arduino :
  https://www.arduino.cc/en/Tutorial/CharacterAnalysis
  https://www.arduino.cc/reference/en/language/variables/data-types/stringobject/
  

  introduction à lufa:
  https://www.engineersgarage.com/article/introduction-lufa
  
  Résumé bibliothèque lufa par Redon:
  https://rex.plil.fr/Enseignement/Systeme/Systeme.IMA4/
  
  Projet IMA4 : LUFA en souris;
  https://projets-ima.plil.fr/mediawiki/index.php/IMA4_2016/2017_ECP3
  
  
  Infos protocole usb:
  http://www.rennes.supelec.fr/ren/fi/elec/docs/usb/usb.html
  
  USB : classe HID (Human Interface Device):
  http://www.rennes.supelec.fr/ren/fi/elec/docs/usb/hid.html
  
  µprojet clavier lufa hid atmega16u2:
  http://fab.cba.mit.edu/classes/863.14/people/andrew_mao/week11/
  
  usb lufa:

  https://www.engineersgarage.com/contribution/atmega-32u4-based-generic-usb-keyboard
  
  Aide possible compilation LUFA:
  https://electronics.stackexchange.com/questions/24512/make-lufa-for-arduino-uno-atmega16u2