Added a makefile to build the project

Makefile

+
+default: centr
+
+buf.o: buf.c
+	gcc -c buf.c -o buf.o
+
+pages.o: pages.asm
+	gcc -c -x assembler pages.asm -o pages.o
+
+install:
+	install centr /usr/bin/centr
+
+clean:
+	rm *.o
+	rm centr
+
+centr: buf.o pages.o centr.c
+	gcc centr.c buf.o pages.o -o centr
+