Create basic, rule-based solver

Makefile

@@ -17,7 +17,7 @@
 CFLAGS += -std=c11 -pedantic -Wall -Wextra
 CFLAGS += -O2 -flto
 
-SRC = main.c sud.c
+SRC = main.c sud.c solve.c
 OBJ = $(SRC:.c=.o)
 
 sudoku: $(OBJ)
@@ -26,7 +26,8 @@ sudoku: $(OBJ)
 clean:
 	rm -f sudoku $(OBJ)
 
-main.o: sud.h
+main.o: sud.h solve.h
 sud.o: sud.h
+solve.o: solve.h
 
 .PHONY: clean