Copter: #define for initial altitude jump during take-off

Developers can add a line like to APM_Config.h to reduce the initial
jump when taking off in Loiter or AltHold flightmodes:
#define ALT_HOLD_TAKEOFF_JUMP 0

ArduCopter/Attitude.pde

@@ -985,7 +985,7 @@ set_throttle_takeoff()
 {
     // set alt target
     if (controller_desired_alt < current_loc.alt) {
-        controller_desired_alt = current_loc.alt + 20;
+        controller_desired_alt = current_loc.alt + ALT_HOLD_TAKEOFF_JUMP;
     }
     // clear i term from acceleration controller
     if (g.pid_throttle_accel.get_integrator() < 0) {

ArduCopter/config.h

@@ -920,7 +920,7 @@
 // Autopilot rotate rate limits
 //
 #ifndef AUTO_YAW_SLEW_RATE
- # define AUTO_YAW_SLEW_RATE        60                     // degrees/sec
+ # define AUTO_YAW_SLEW_RATE    60              // degrees/sec
 #endif
 
 
@@ -928,11 +928,15 @@
 // Throttle control gains
 //
 #ifndef THROTTLE_CRUISE
- # define THROTTLE_CRUISE       450            //
+ # define THROTTLE_CRUISE       450             // default estimate of throttle required for vehicle to maintain a hover
 #endif
 
 #ifndef THR_MID
- # define THR_MID        500                            // Throttle output (0 ~ 1000) when throttle stick is in mid position
+ # define THR_MID               500             // Throttle output (0 ~ 1000) when throttle stick is in mid position
+#endif
+
+#ifndef ALT_HOLD_TAKEOFF_JUMP
+ # define ALT_HOLD_TAKEOFF_JUMP 20              // jump in altitude target when taking off in Loiter or AltHold flight modes
 #endif
 
 #ifndef ALT_HOLD_P
@@ -964,7 +968,6 @@
 #ifndef PILOT_VELZ_MAX
  # define PILOT_VELZ_MAX    250     // maximum vertical velocity in cm/s
 #endif
-#define ACCELERATION_MAX_Z  750     // maximum veritcal acceleration in cm/s/s
 
 // max distance in cm above or below current location that will be used for the alt target when transitioning to alt-hold mode
 #ifndef ALT_HOLD_INIT_MAX_OVERSHOOT