Implement `sub`

logisim/nano.circ

@@ -291,7 +291,7 @@
     <comp lib="4" loc="(470,570)" name="ROM">
       <a name="contents">addr/data: 8 8
 40 81 62 ee 85 81 84 0
-0 1 2 1
+0 1 2 1 10 12 11 11
 </a>
     </comp>
     <comp lib="0" loc="(370,660)" name="Tunnel">
@@ -458,7 +458,7 @@
       <a name="addrWidth" val="4"/>
       <a name="dataWidth" val="12"/>
       <a name="contents">addr/data: 4 12
-300 7*0 380
+300 340 6*0 380
 </a>
     </comp>
     <comp lib="0" loc="(220,610)" name="Tunnel">