demo: Rename zahnrad binaries to demo

demo/rawfb/x11/Makefile

@@ -1,5 +1,5 @@
 # Install
-BIN = zahnrad
+BIN = demo
 
 # Flags
 CFLAGS += -std=c89 -Wall -Wextra -pedantic -Wno-unused-function -O2

demo/x11/Makefile

@@ -1,5 +1,5 @@
 # Install
-BIN = zahnrad
+BIN = demo
 
 # Flags
 CFLAGS += -std=c89 -Wall -Wextra -pedantic -Wno-unused-function -O2

demo/x11_xft/Makefile

@@ -1,5 +1,5 @@
 # Install
-BIN = zahnrad
+BIN = demo
 
 # Flags
 CFLAGS += -std=c89 -Wall -Wextra -pedantic -Wno-unused-function -O2