Resolve "Add peek function"

Closes #7 (closed)

stack.c

+<<<<<<< HEAD
+#include <stdio.h>
 #include "stack.h"
+
+void peek(stack s, int *value){
+    if(s.top>-1 && s.top<s.capacity){
+        *value=s.data[s.top];
+    }
+}
+=======
+#include "stack.h"
+>>>>>>> main