moves out the file functions into their own file

src/Makefile

@@ -1,15 +1,16 @@
 TARGET=xxd
 CC=gcc
 
-OBJ = main.o hex.o
+OBJ = main.o hex.o file.o
 
 $(TARGET): $(OBJ)
 	mkdir -p ../build
 	$(CC) -Wall -g -o $(TARGET) $(OBJ) -g
 	mv $(TARGET) ../build/
 
-main.o: include/hex.h
+main.o: include/hex.h include/file.h
 hex.o: include/hex.h
+file.o: include/file.h
 
 .PHONY: clean
 clean: