set set-drone(name) set-drone
set set-drone(short) sdro
set set-drone(purpose) {set drone volume}
set set-drone(invoke) {set-drone OR sdro volume OR v <list of drone ids> <list of volumes>}
set set-drone(help) {
  drone id must be > -1

  volume is in range 0 to 1 but not enforced.
  }
set set-drone(examples) {
  set-drone volume 0 0.7 ;# set volume of drone 0 ie 1st drone to 0.7
  sdro v 1 -1 ;# set volume of drone 1 ie 2nd drone to -1 --> reverse phase
  set-drone volume {0 1 2} 0 ;# silence first 3 drones
  set-drone volume {0 1 2} {0 0.1 0.2} ;# first 3 drones assigned volumes 0, 0.1 and 0.2}