VARIO_EXTENDED new feature

Limits changed:
Down speed min in range OFF,[-10.0:0] in 0.1 steps
OFF means no sound at all, this variant useful if pilot/model is aerobatic
Up speed min in range [-1.5:1.5] in 0.1 steps
strange negative values for positive vertical speeds means next:
in normal fly glider model has negative speed always, for example -1m/s
if any weak thermal flows found then vertical speed can be reduced but still negative, but it is symptom of thermal flow which can be very close!
now it is possible to detect if negative Up speed limit is set.

src/frsky.h

@@ -73,7 +73,7 @@ class FrskyData: public FrskyRSSI {
 #define VARIO_SPEED_LIMIT_MUL       10 //to get 0.2m steps
 #define VARIO_SPEED_LIMIT_DOWN_OFF  (100+1) //100 steps + OFF
 #define VARIO_SPEED_LIMIT_UP_CENTER 15
-#define VARIO_SPEED_LIMIT_UP_MAX    31
+#define VARIO_SPEED_LIMIT_UP_MAX    30
 
 #if defined(FRSKY_HUB)
 PACK(struct FrskyHubData {