Makefile: simplification and improvment

Default target is the main program.
Use implicit rule for main program.
Generate .d file at compilation time instead of using specific rules
Fix CFLAGS CPPFLAGS usage

Makefile/Makefile

@@ -1,19 +1,23 @@
-CPPFLAGS ?= -Werror -Wall
+# Preproc options
+# -MMD is used to generate .d files for header dependencies
+CPPFLAGS = -MMD
+# main compilation
+CFLAGS ?= -Werror -Wall
+#Linker flags
+LDFLAGS =
+#Linker path
+LDLIBS =
 
 program = test
 sources = $(wildcard *.c)
 objects = $(sources:%.c=%.o)
 depends = $(sources:%.c=%.d)
 
-%.d: %.c
-	@$(CPP) $(CPPFLAGS) -c -MP -MM -MT "$@ $*.o" $< >$@
-
 $(program): $(objects)
-	$(CXX) -o $@ $^ $(LDFLAGS) $(LDLIBS)
 
 .PHONY: clean
 clean:
-	rm -f $(program) $(objects) $(depends)
+	$(RM) $(program) $(objects) $(depends)
 
 ifneq ($(MAKECMDGOALS),clean)
 -include $(depends)