Resolve "Add pop function"

Closes #6 (closed)

Makefile

-CC=gcc
-CFLAGS=-Wall -Wextra -pedantic -g -std=c11 -O3
-CFLAGS_ASAN=-fsanitize=address -fno-omit-frame-pointer
-LDFLAGS=-lm
-LDFLAGS_ASAN=-fsanitize=address -fno-omit-frame-pointer
-
-main: stack.o main.o
-	$(CC) -o $@ $^ $(CFLAGS) $(LDFLAGS) $(LDFLAGS_ASAN)
-
-%.o: %.c 
-	$(CC) $(CFLAGS) $(CFLAGS_ASAN) -c $^ -o $@
-
-clean:
-	rm -f *.o main