GPS fix level: support higher than 3
mavproxy_rc: rc command gracefully handles invalid pwmvalues
mavproxy_cmdlng added and cmd guided with lat/lon param upgraded
CMD_CONDITION_YAW added in mavproxy_cmdllong
Adding take off command long
Adding altitude management in takeoff cmd
cmdlong: rename speed and yaw to setspeed and setyaw
mode: fixed guided mode change for current module structure
release 1.3.6
rc: expose set_override for use by other modules

Rather than sending rc_override msgs straight from droneapi goo I'd
rather just share this code (so they don't develop disagreements about
desired rc state)
raise version
moved battery handling to its own module
elevation: return None on bad elevation
cope with None return from elevation module
terrain: first version of terrain module
terrain: enable terrain module by default
Checklist module updated and operational