title: How to change altitude in Drone API
body: <p>Pleas help me to understand ho to change altitude in drone API. I can not find information about that. Even in source code.</p>
  
  <p>I have a simple project, drone must do a few movements. Arm the motors (of course with preflight check), takeoff on 10 meters, wait 20 sec. and climb to 20 meters.</p>
  
  <p>So what function do I use to force my multi-rotor climb in 20 meters, or go down in 5 meters?</p>
  
  <p>And tell me please a similar 'cmd'command for MAVProxy. </p>