doc/common/conf: Display s^2 units correctly.

Now that we no longer use these in hyperlinks, we can use the right
unicode to display this unit correctly.

doc/common/conf.py

@@ -314,10 +314,10 @@ def on_missing_reference(app, env, node, contnode):
     for unit in [
         "deg",
         "deg/s",
-        "deg/s/s",
+        "deg/s²",
         "mm",
         "mm/s",
-        "mm/s/s",
+        "mm/s²",
         "%",
         "mV",
         "mA",

doc/main/hubs/movehub.rst

@@ -29,7 +29,7 @@ Move Hub
 
         .. versionchanged:: 3.2
 
-            Changed acceleration units from m/s/s to mm/s/s.
+            Changed acceleration units from m/s² to mm/s².
 
     .. rubric:: Using the battery
 

doc/main/signaltypes.rst

@@ -76,12 +76,12 @@ use the following table to convert between commonly used units.
 
 .. _acceleration:
 
-rotational acceleration: deg/s/s
+rotational acceleration: deg/s²
 --------------------------------
 
 Rotational acceleration, or *angular acceleration* describes how fast the
 rotational speed changes. This is expressed as the change of the number of
-degrees per second, during one second (deg/s/s). This is also commonly written
+degrees per second, during one second (deg/s²). This is also commonly written
 as  :math:`deg/s^2`.
 
 For example, you can adjust the rotational acceleration setting of a ``Motor``
@@ -134,11 +134,11 @@ For example, the speed of a robotic vehicle is expressed in mm/s.
 
 .. _linacceleration:
 
-linear acceleration: mm/s/s
+linear acceleration: mm/s²
 --------------------------------
 
 Linear acceleration describes how fast the speed changes. This is expressed as
-the change of the millimeters per second, during one second (mm/s/s).
+the change of the millimeters per second, during one second (mm/s²).
 This is also commonly written as  :math:`mm/s^2`.
 
 For example, you can adjust the acceleration setting of a