Change stackup.

Top layer is now 3.3V pour + signals
Middle layers are now ground.
Bottom layer is now 5.0V pour + signals

Setting both middle layers to ground means every signal
gets a high quality return path, reducing loop area and
hopefully reducing EMI.

Author: jonathanpallant

Kicad/bmc.kicad_sch

@@ -1297,6 +1297,7 @@
     )
   )
 
+
   (junction (at 132.715 36.83) (diameter 0) (color 0 0 0 0)
     (uuid 082e206e-c9c7-4fb1-8a3c-059104b33497)
   )