Build the BS-SPEKE code as a library

Makefile

 default: demo
 
+lib: libbsspeke.a
+
 minimonocypher.o: minimonocypher.c minimonocypher.h
 	cc -c minimonocypher.c
 
@@ -9,8 +11,11 @@ bsspeke.o: bsspeke.c bsspeke.h minimonocypher.h
 demo.o: demo.c bsspeke.h
 	cc -c demo.c
 
-demo: demo.o bsspeke.o minimonocypher.o
-	cc -o demo demo.o bsspeke.o minimonocypher.o
+demo: demo.o libbsspeke.a
+	cc -o demo demo.o -L. -lbsspeke
+
+libbsspeke.a: bsspeke.o minimonocypher.o
+	ar rcs libbsspeke.a bsspeke.o minimonocypher.o
 
 clean:
-	rm -f demo bsspeke.o minimonocypher.o
+	rm -f demo bsspeke.o minimonocypher.o libbsspeke.a