https://github.com/ArduPilot/ardupilot/pull/5135

Using a global .dir-locals.el file is a better alternative than
reincluding the same emacs header in every file of the project.

this allows for automatic engine start and restart

this also adds the g2 parameter table

text revisions

Plane uniformization of severities

- moved terrain alt rangefinder power-off trigger from trerrain thread to rangefinder thread
- allow rangefinder to power-off using baro if terrain data not available

The PSTR is already define as a NOP for all supported platforms. It's
only needed for AVR so here we remove all the uses throughout the
codebase.

This was automated with a simple python script so it also converts
places which spans to multiple lines, removing the matching parentheses.

AVR-specific places were not changed.

useful for seeing if a petrol motor is still running

Plane: Moving to RSSI library for reading various kinds of RSSI, with the possibility of adding more.

* Retains ability to read from Analog Pin
* Adds ability to read RSSI from PWM channel value as is done in OpenLRSng, EazyUHF, and various other LRS.
* Handles any type of RSSI that provides RSSI values inverted - i.e. when the low value is the best signal and the high value is the worst signal.
* Has different key names from all existing RSSI parameters to provide for a clean break and easier distinguishing.
* Existing parameters are marked as obsolete

this saves 5k of flash space, enough for support to be kept for
another release

this calculates the aerodymanic load factor from smoothed airspeed and
uses it to limit roll to keep it below the level where the load factor
would take us past the aerodymanic limit of the airframe

this allows short outages to be ridden out

only accept data when we have had 10 samples in a row in range at 50Hz

when enabled RTL, CRUISE and rally points will use terrain altitude

including raw temperature and pressure values

use safety switch if arming not enabled