AC_AttitudeControl: Use SI units conventions in parameter units

Follow the rules from:
http://physics.nist.gov/cuu/Units/units.html
http://physics.nist.gov/cuu/Units/outside.html
and
http://physics.nist.gov/cuu/Units/checklist.html
one further constrain is that only printable (7bit) ASCII characters are allowed

libraries/AC_AttitudeControl/AC_AttitudeControl.cpp

@@ -10,7 +10,7 @@ const AP_Param::GroupInfo AC_AttitudeControl::var_info[] = {
     // @Param: SLEW_YAW
     // @DisplayName: Yaw target slew rate
     // @Description: Maximum rate the yaw target can be updated in Loiter, RTL, Auto flight modes
-    // @Units: Centi-Degrees/Sec
+    // @Units: cdeg/s
     // @Range: 500 18000
     // @Increment: 100
     // @User: Advanced
@@ -21,7 +21,7 @@ const AP_Param::GroupInfo AC_AttitudeControl::var_info[] = {
     // @Param: ACCEL_Y_MAX
     // @DisplayName: Acceleration Max for Yaw
     // @Description: Maximum acceleration in yaw axis
-    // @Units: Centi-Degrees/Sec/Sec
+    // @Units: cdeg/s/s
     // @Range: 0 72000
     // @Values: 0:Disabled, 18000:Slow, 36000:Medium, 54000:Fast
     // @Increment: 1000
@@ -38,7 +38,7 @@ const AP_Param::GroupInfo AC_AttitudeControl::var_info[] = {
     // @Param: ACCEL_R_MAX
     // @DisplayName: Acceleration Max for Roll
     // @Description: Maximum acceleration in roll axis
-    // @Units: Centi-Degrees/Sec/Sec
+    // @Units: cdeg/s/s
     // @Range: 0 180000
     // @Increment: 1000
     // @Values: 0:Disabled, 72000:Slow, 108000:Medium, 162000:Fast
@@ -48,7 +48,7 @@ const AP_Param::GroupInfo AC_AttitudeControl::var_info[] = {
     // @Param: ACCEL_P_MAX
     // @DisplayName: Acceleration Max for Pitch
     // @Description: Maximum acceleration in pitch axis
-    // @Units: Centi-Degrees/Sec/Sec
+    // @Units: cdeg/s/s
     // @Range: 0 180000
     // @Increment: 1000
     // @Values: 0:Disabled, 72000:Slow, 108000:Medium, 162000:Fast

libraries/AC_AttitudeControl/AC_AttitudeControl_Heli.cpp

@@ -16,7 +16,7 @@ const AP_Param::GroupInfo AC_AttitudeControl_Heli::var_info[] = {
     // @Param: HOVR_ROL_TRM
     // @DisplayName: Hover Roll Trim
     // @Description: Trim the hover roll angle to counter tail rotor thrust in a hover
-    // @Units: Centi-Degrees
+    // @Units: cdeg
     // @Range: 0 1000
     // @User: Advanced
     AP_GROUPINFO("HOVR_ROL_TRM",    1, AC_AttitudeControl_Heli, _hover_roll_trim, AC_ATTITUDE_HELI_HOVER_ROLL_TRIM_DEFAULT),

libraries/AC_AttitudeControl/AC_AttitudeControl_Multi.cpp

@@ -26,7 +26,7 @@ const AP_Param::GroupInfo AC_AttitudeControl_Multi::var_info[] = {
     // @Description: Roll axis rate controller I gain maximum.  Constrains the maximum motor output that the I gain will output
     // @Range: 0 1
     // @Increment: 0.01
-    // @Units: Percent
+    // @Units: %
     // @User: Standard
 
     // @Param: RAT_RLL_D
@@ -71,7 +71,7 @@ const AP_Param::GroupInfo AC_AttitudeControl_Multi::var_info[] = {
     // @Description: Pitch axis rate controller I gain maximum.  Constrains the maximum motor output that the I gain will output
     // @Range: 0 1
     // @Increment: 0.01
-    // @Units: Percent
+    // @Units: %
     // @User: Standard
 
     // @Param: RAT_PIT_D
@@ -116,7 +116,7 @@ const AP_Param::GroupInfo AC_AttitudeControl_Multi::var_info[] = {
     // @Description: Yaw axis rate controller I gain maximum.  Constrains the maximum motor output that the I gain will output
     // @Range: 0 1
     // @Increment: 0.01
-    // @Units: Percent
+    // @Units: %
     // @User: Standard
 
     // @Param: RAT_YAW_D

libraries/AC_AttitudeControl/AC_AttitudeControl_Sub.cpp

@@ -26,7 +26,7 @@ const AP_Param::GroupInfo AC_AttitudeControl_Sub::var_info[] = {
     // @Description: Roll axis rate controller I gain maximum.  Constrains the maximum motor output that the I gain will output
     // @Range: 0 1
     // @Increment: 0.01
-    // @Units: Percent
+    // @Units: %
     // @User: Standard
 
     // @Param: RAT_RLL_D
@@ -71,7 +71,7 @@ const AP_Param::GroupInfo AC_AttitudeControl_Sub::var_info[] = {
     // @Description: Pitch axis rate controller I gain maximum.  Constrains the maximum motor output that the I gain will output
     // @Range: 0 1
     // @Increment: 0.01
-    // @Units: Percent
+    // @Units: %
     // @User: Standard
 
     // @Param: RAT_PIT_D
@@ -116,7 +116,7 @@ const AP_Param::GroupInfo AC_AttitudeControl_Sub::var_info[] = {
     // @Description: Yaw axis rate controller I gain maximum.  Constrains the maximum motor output that the I gain will output
     // @Range: 0 1
     // @Increment: 0.01
-    // @Units: Percent
+    // @Units: %
     // @User: Standard
 
     // @Param: RAT_YAW_D