Add CP/NET Serial Interface Client Files

- Generic serial interface client support files have been added.  This mode of operation is not documented in the RomWBW User Guide.  Refer to <https://github.com/durgadas311/cpnet-z80>.
- Minor patch to NULU so it does not spit out a directory listing every time it is invoked.

Source/CPNET/Build.cmd

@@ -10,5 +10,7 @@ zxcc nulu --O -cpn12mt "-<30" --A mt011/cpnet12/*.* --L --X || exit /b
 zxcc nulu --O -cpn3mt "-<30" --A mt011/cpnet3/*.* --L --X || exit /b
 zxcc nulu --O -cpn12duo "-<30" --A duo/cpnet12/*.* --L --X || exit /b
 zxcc nulu --O -cpn3duo "-<30" --A duo/cpnet3/*.* --L --X || exit /b
+zxcc nulu --O -cpn12ser "-<30" --A serial/cpnet12/*.* --L --X || exit /b
+zxcc nulu --O -cpn3ser "-<30" --A serial/cpnet3/*.* --L --X || exit /b
 
 copy *.lbr ..\..\Binary\CPNET

Source/CPNET/Makefile

@@ -1,4 +1,4 @@
-OBJECTS = cpn12mt.lbr cpn3mt.lbr cpn12duo.lbr cpn3duo.lbr
+OBJECTS = cpn12mt.lbr cpn3mt.lbr cpn12duo.lbr cpn3duo.lbr cpn12ser.lbr cpn3ser.lbr
 DEST = ../../Binary/CPNET/
 TOOLS = ../../Tools
 
@@ -8,6 +8,7 @@ cpn12%.lbr: CPNETVER=cpnet12
 cpn3%.lbr: CPNETVER=cpnet3
 %mt.lbr: HWVER=mt011
 %duo.lbr: HWVER=duo
+%ser.lbr: HWVER=serial
 
 %.lbr:
 	rm -f $@