Fix roll correction, closes #1

source/imu.cpp

@@ -35,6 +35,8 @@ void calibrateGyroBias() {
   biasGZ = (float)(sz/BIAS_SAMPLES);
   calTempC = readIMUTemp();
   angleX = angleY = accumX = accumY = 0.0f;
+  // Seed gravity estimate from current accel so projection is correct immediately
+  gravX = imu.readFloatAccelX(); gravY = imu.readFloatAccelY(); gravZ = imu.readFloatAccelZ();
 
   #ifdef FEATURE_TELEMETRY
     statRecalCount++;