Improve how to redefine macros in 2001/kev

Now one can do

    make clobber PORT=37337 SPEED=50 everything

The l_ macro can also be redefined with the 'L' variable but this is not
recommended especially if you don't know what you're doing so it's
barely mentioned in the README.md file.

2001/kev/Makefile

@@ -57,9 +57,15 @@ CSTD= -std=gnu99
 #
 ARCH=
 
+# variables for the macros for easier redefining
+#
+PORT= 5455
+SPEED= 100
+L= "socket(il.sin_family=AF_INET,SOCK_STREAM,0)"
+
 # Defines that are needed to compile
 #
-CDEFINE= -DPORT=5455 -DSPEED=100 -Dl_="socket(il.sin_family=AF_INET,SOCK_STREAM,0)"
+CDEFINE= -DPORT=${PORT} -DSPEED=${SPEED} -Dl_=${L}
 
 # Include files that are needed to compile
 #