[radio control] spektrum also usable for intermcu
[build] don't error on clean if cross-compiler is not found
[maps] use BRE instead of extended regex for sed
[build] use pkg-config to find ivy-glib
[build] use pkg-config to get ivy include dirs for simulation targets
[logalizer] remove cruft and fix compilation of disp3d

maybe just remove disp3d and some of the other remaining stuff as well...
[math] pprz_isa: QNH functions
[air_data] use ABI for differential pressure, compute airspeed from it
[air_data] add qnh and amsl
[modules] make air_data a module
[airframes] add air_data module to some example airframes
[air_data] add TEMPERATURE ABI message and calc true airspeed

- removed airspeed_scale
- true airspeed (TAS) factor calculated from pressure and temp
  - if that is not available, tas_factor can be set manually (and could be used to replace airspeed_scale
[modules] USE_AIRSPEED_AIR_DATA flag

so you can let it calc the airspeed without pushing it to the state interface,
e.g. to use a different airspeed sensor for state interface and hence control
[messages][modules] add AIR_DATA message
[modules] initialize air_data variables
[modules] fix ABI subscription for BARO_DIFF
[modules] update air_data doc
[ctrl] Energy control > 50hours of test. Proven. Remove warning.

closes #869
[gps] Outback safety rules demand actions upon loss of GPS, but one still must be able to startup

closes #868
[airspeed_adc] Calibrate inflight